In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, e ...
, a database is an organized collection of
data
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted ...
stored and accessed electronically. Small databases can be stored on a
file system
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
, while large databases are hosted on
computer clusters
A computer cluster is a set of computers that work together so that they can be viewed as a single system. Unlike grid computers, computer clusters have each node set to perform the same task, controlled and scheduled by software.
The comp ...
or
cloud storage
Cloud storage is a model of computer data storage in which the digital data is stored in logical pools, said to be on "the cloud". The physical storage spans multiple servers (sometimes in multiple locations), and the physical environment is t ...
. The
design of databases spans formal techniques and practical considerations, including
data modeling
Data modeling in software engineering is the process of creating a data model for an information system by applying certain formal techniques.
Overview
Data modeling is a process used to define and analyze data requirements needed to suppo ...
, efficient data representation and storage,
query language
Query languages, data query languages or database query languages (DQL) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Types
Broadly, query language ...
s,
security
Security is protection from, or resilience against, potential harm (or other unwanted coercive change) caused by others, by restraining the freedom of others to act. Beneficiaries (technically referents) of security may be of persons and social ...
and
privacy
Privacy (, ) is the ability of an individual or group to seclude themselves or information about themselves, and thereby express themselves selectively.
The domain of privacy partially overlaps with security, which can include the concepts of a ...
of sensitive data, and
distributed computing
A distributed system is a system whose components are located on different computer network, networked computers, which communicate and coordinate their actions by message passing, passing messages to one another from any system. Distributed com ...
issues, including supporting
concurrent
Concurrent means happening at the same time. Concurrency, concurrent, or concurrence may refer to:
Law
* Concurrence, in jurisprudence, the need to prove both ''actus reus'' and ''mens rea''
* Concurring opinion (also called a "concurrence"), a ...
access and
fault tolerance
Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
.
A
database management system
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases span ...
(DBMS) is the
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
that interacts with
end user
In product development, an end user (sometimes end-user) is a person who ultimately uses or is intended to ultimately use a product. The end user stands in contrast to users who support or maintain the product, such as sysops, system administrat ...
s, applications, and the database itself to capture and analyze the data. The DBMS software additionally encompasses the core facilities provided to administer the database. The sum total of the database, the DBMS and the associated applications can be referred to as a database system. Often the term "database" is also used loosely to refer to any of the DBMS, the database system or an application associated with the database.
Computer scientists
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to practical disciplines (including th ...
may classify database management systems according to the
database model
A database model is a type of data model that determines the logical structure of a database. It fundamentally determines in which manner data can be stored, organized and manipulated. The most popular example of a database model is the relational ...
s that they support.
Relational database
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...
s became dominant in the 1980s. These model data as
rows and
columns
A column or pillar in architecture and structural engineering is a structural element that transmits, through compression, the weight of the structure above to other structural elements below. In other words, a column is a compression member. ...
in a series of
tables
Table may refer to:
* Table (furniture), a piece of furniture with a flat surface and one or more legs
* Table (landform), a flat area of land
* Table (information), a data arrangement with rows and columns
* Table (database), how the table data ...
, and the vast majority use
SQL for writing and querying data. In the 2000s, non-relational databases became popular, collectively referred to as
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed ...
, because they use different
query language
Query languages, data query languages or database query languages (DQL) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Types
Broadly, query language ...
s.
Terminology and overview
Formally, a "database" refers to a set of related data and the way it is organized. Access to this data is usually provided by a "database management system" (DBMS) consisting of an integrated set of computer software that allows
users
Ancient Egyptian roles
* User (ancient Egyptian official), an ancient Egyptian nomarch (governor) of the Eighth Dynasty
* Useramen, an ancient Egyptian vizier also called "User"
Other uses
* User (computing), a person (or software) using an ...
to interact with one or more databases and provides access to all of the data contained in the database (although restrictions may exist that limit access to particular data). The DBMS provides various functions that allow entry, storage and retrieval of large quantities of information and provides ways to manage how that information is organized.
Because of the close relationship between them, the term "database" is often used casually to refer to both a database and the DBMS used to manipulate it.
Outside the world of professional
information technology
Information technology (IT) is the use of computers to create, process, store, retrieve, and exchange all kinds of data . and information. IT forms part of information and communications technology (ICT). An information technology system (I ...
, the term ''database'' is often used to refer to any collection of related data (such as a
spreadsheet
A spreadsheet is a computer application for computation, organization, analysis and storage of data in tabular form. Spreadsheets were developed as computerized analogs of paper accounting worksheets. The program operates on data entered in cel ...
or a card index) as size and usage requirements typically necessitate use of a database management system.
Existing DBMSs provide various functions that allow management of a database and its data which can be classified into four main functional groups:
* Data definition – Creation, modification and removal of definitions that define the organization of the data.
* Update – Insertion, modification, and deletion of the actual data.
* Retrieval – Providing information in a form directly usable or for further processing by other applications. The retrieved data may be made available in a form basically the same as it is stored in the database or in a new form obtained by altering or combining existing data from the database.
* Administration – Registering and monitoring users, enforcing data security, monitoring performance, maintaining data integrity, dealing with concurrency control, and recovering information that has been corrupted by some event such as an unexpected system failure.
Both a database and its DBMS conform to the principles of a particular
database model
A database model is a type of data model that determines the logical structure of a database. It fundamentally determines in which manner data can be stored, organized and manipulated. The most popular example of a database model is the relational ...
. "Database system" refers collectively to the database model, database management system, and database.
Physically, database
servers are dedicated computers that hold the actual databases and run only the DBMS and related software. Database servers are usually
multiprocessor
Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system. The term also refers to the ability of a system to support more than one processor or the ability to allocate tasks between them. There ar ...
computers, with generous memory and
RAID
Raid, RAID or Raids may refer to:
Attack
* Raid (military), a sudden attack behind the enemy's lines without the intention of holding ground
* Corporate raid, a type of hostile takeover in business
* Panty raid, a prankish raid by male college ...
disk arrays used for stable storage. Hardware database accelerators, connected to one or more servers via a high-speed channel, are also used in large volume
transaction processing environments. DBMSs are found at the heart of most
database application
A database application is a computer program whose primary purpose is retrieving information from a computerized database. From here, information can be inserted, modified or deleted which is subsequently conveyed back into the database. Early e ...
s. DBMSs may be built around a custom
multitasking kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learnin ...
with built-in
networking support, but modern DBMSs typically rely on a standard
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...
to provide these functions.
Since DBMSs comprise a significant
market
Market is a term used to describe concepts such as:
*Market (economics), system in which parties engage in transactions according to supply and demand
*Market economy
*Marketplace, a physical marketplace or public market
Geography
*Märket, an ...
, computer and storage vendors often take into account DBMS requirements in their own development plans.
Databases and DBMSs can be categorized according to the database model(s) that they support (such as
relational or
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
), the type(s) of computer they run on (from a
server cluster to a
mobile phone
A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whil ...
), the
query language
Query languages, data query languages or database query languages (DQL) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Types
Broadly, query language ...
(s) used to access the database (such as SQL or
XQuery
XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, bin ...
), and their internal engineering, which affects performance,
scalability
Scalability is the property of a system to handle a growing amount of work by adding resources to the system.
In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a ...
, resilience, and security.
History
The sizes, capabilities, and performance of databases and their respective DBMSs have grown in orders of magnitude. These performance increases were enabled by the technology progress in the areas of
processors
A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...
,
computer memory
In computing, memory is a device or system that is used to store information for immediate use in a computer or related computer hardware and digital electronic devices. The term ''memory'' is often synonymous with the term ''primary storage ...
,
computer storage
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
The central processing unit (CPU) of a compute ...
, and
computer network
A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...
s. The concept of a database was made possible by the emergence of direct access storage media such as magnetic disks, which became widely available in the mid-1960s; earlier systems relied on sequential storage of data on magnetic tape. The subsequent development of database technology can be divided into three eras based on data model or structure:
navigational
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
, SQL/
relational, and post-relational.
The two main early navigational data models were the
hierarchical model
A hierarchical database model is a data model in which the data are organized into a tree-like structure. The data are stored as records which are connected to one another through links. A record is a collection of fields, with each field containin ...
and the
CODASYL
CODASYL, the Conference/Committee on Data Systems Languages, was a consortium formed in 1959 to guide the development of a standard programming language that could be used on many computers. This effort led to the development of the programming l ...
model (
network model
The network model is a database model conceived as a flexible way of representing objects and their relationships. Its distinguishing feature is that the schema, viewed as a graph in which object types are nodes and relationship types are arcs, ...
). These were characterized by the use of pointers (often physical disk addresses) to follow relationships from one record to another.
The
relational model
The relational model (RM) is an approach to managing data using a Structure (mathematical logic), structure and language consistent with first-order logic, first-order predicate logic, first described in 1969 by English computer scientist Edgar F. ...
, first proposed in 1970 by
Edgar F. Codd
Edgar Frank "Ted" Codd (19 August 1923 – 18 April 2003) was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases and relational databa ...
, departed from this tradition by insisting that applications should search for data by content, rather than by following links. The relational model employs sets of ledger-style tables, each used for a different type of entity. Only in the mid-1980s did computing hardware become powerful enough to allow the wide deployment of relational systems (DBMSs plus applications). By the early 1990s, however, relational systems dominated in all large-scale
data processing
Data processing is the collection and manipulation of digital data to produce meaningful information.
Data processing is a form of ''information processing'', which is the modification (processing) of information in any manner detectable by an ...
applications, and they remain dominant:
IBM Db2
Db2 is a family of data management products, including database servers, developed by IBM. It initially supported the relational model, but was extended to support object–relational features and non-relational structures like JSON a ...
,
Oracle
An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination.
Description
The word '' ...
,
MySQL
MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database o ...
, and
Microsoft SQL Server
Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ma ...
are the most searched
DBMS
In computing, a database is an organized collection of data stored and accessed electronically. Small databases can be stored on a file system, while large databases are hosted on computer clusters or cloud storage. The design of databases spa ...
. The dominant database language, standardized SQL for the relational model, has influenced database languages for other data models.
Object database
An object database or object-oriented database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which ar ...
s were developed in the 1980s to overcome the inconvenience of
object–relational impedance mismatch
The object–relational impedance mismatch is a set of conceptual and technical difficulties that are often encountered when a relational database management system (RDBMS) is being served by an application program (or multiple application progra ...
, which led to the coining of the term "post-relational" and also the development of hybrid
object–relational database
An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inheritan ...
s.
The next generation of post-relational databases in the late 2000s became known as
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed ...
databases, introducing fast
key–value stores and
document-oriented database
A document-oriented database, or document store, is a computer program and data storage system designed for storing, retrieving and managing document-oriented information, also known as semi-structured data.
Document-oriented databases are one ...
s. A competing "next generation" known as
NewSQL
NewSQL is a class of relational database management systems that seek to provide the scalability of NoSQL systems for online transaction processing (OLTP) workloads while maintaining the ACID guarantees of a traditional database system.
Many e ...
databases attempted new implementations that retained the relational/SQL model while aiming to match the high performance of NoSQL compared to commercially available relational DBMSs.
1960s, navigational DBMS
![CodasylB](https://upload.wikimedia.org/wikipedia/commons/d/d6/CodasylB.png)
The introduction of the term ''database'' coincided with the availability of direct-access storage (disks and drums) from the mid-1960s onwards. The term represented a contrast with the tape-based systems of the past, allowing shared interactive use rather than daily
batch processing
Computerized batch processing is a method of running software programs called jobs in batches automatically. While users are required to submit the jobs, no other interaction by the user is required to process the batch. Batches may automatically ...
. The
Oxford English Dictionary
The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a com ...
cites a 1962 report by the System Development Corporation of California as the first to use the term "data-base" in a specific technical sense.
As computers grew in speed and capability, a number of general-purpose database systems emerged; by the mid-1960s a number of such systems had come into commercial use. Interest in a standard began to grow, and
Charles Bachman
Charles William Bachman III (December 11, 1924 – July 13, 2017) was an American computer scientist, who spent his entire career as an industrial researcher, developer, and manager rather than in academia. He was particularly known for his ...
, author of one such product, the
Integrated Data Store
Integrated Data Store (IDS) was an early network database management system largely used by industry, known for its high performance. IDS became the basis for the CODASYL Data Base Task Group standards.
IDS was designed in the 1960s at the ...
(IDS), founded the Database Task Group within
CODASYL
CODASYL, the Conference/Committee on Data Systems Languages, was a consortium formed in 1959 to guide the development of a standard programming language that could be used on many computers. This effort led to the development of the programming l ...
, the group responsible for the creation and standardization of
COBOL
COBOL (; an acronym for "common business-oriented language") is a compiled English-like computer programming language designed for business use. It is an imperative, procedural and, since 2002, object-oriented language. COBOL is primarily us ...
. In 1971, the Database Task Group delivered their standard, which generally became known as the ''CODASYL approach'', and soon a number of commercial products based on this approach entered the market.
The CODASYL approach offered applications the ability to navigate around a linked data set which was formed into a large network. Applications could find records by one of three methods:
#Use of a primary key (known as a CALC key, typically implemented by
hashing
Hash, hashes, hash mark, or hashing may refer to:
Substances
* Hash (food), a coarse mixture of ingredients
* Hash, a nickname for hashish, a cannabis product
Hash mark
* Hash mark (sports), a marking on hockey rinks and gridiron football fiel ...
)
#Navigating relationships (called ''sets'') from one record to another
#Scanning all the records in a sequential order
Later systems added
B-tree
In computer science, a B-tree is a self-balancing tree data structure that maintains sorted data and allows searches, sequential access, insertions, and deletions in logarithmic time. The B-tree generalizes the binary search tree, allowing for n ...
s to provide alternate access paths. Many CODASYL databases also added a declarative query language for end users (as distinct from the navigational API). However, CODASYL databases were complex and required significant training and effort to produce useful applications.
IBM also had its own DBMS in 1966, known as
Information Management System
The IBM Information Management System (IMS) is a joint hierarchical database and information management system that supports transaction processing.
History
IBM designed the IMS with Rockwell and Caterpillar starting in 1966 for the Apollo pr ...
(IMS). IMS was a development of software written for the
Apollo program on the
System/360
The IBM System/360 (S/360) is a family of mainframe computer systems that was announced by IBM on April 7, 1964, and delivered between 1965 and 1978. It was the first family of computers designed to cover both commercial and scientific applica ...
. IMS was generally similar in concept to CODASYL, but used a strict hierarchy for its model of data navigation instead of CODASYL's network model. Both concepts later became known as navigational databases due to the way data was accessed: the term was popularized by Bachman's 1973
Turing Award
The ACM A. M. Turing Award is an annual prize given by the Association for Computing Machinery (ACM) for contributions of lasting and major technical importance to computer science. It is generally recognized as the highest distinction in compu ...
presentation ''The Programmer as Navigator''. IMS is classified by IBM as a
hierarchical database
A hierarchical database model is a data model in which the data are organized into a tree-like structure. The data are stored as records which are connected to one another through links. A record is a collection of fields, with each field containin ...
. IDMS and
Cincom Systems
Cincom Systems, Inc., is a Private company, privately held multinational computer technology corporation founded in 1968 by Tom Nies, Tom Richley, and Claude Bogardus.
The company's best known product today is named Total (trademark ''TOTAL''). ...
'
TOTAL databases are classified as network databases. IMS remains in use .
1970s, relational DBMS
Edgar F. Codd
Edgar Frank "Ted" Codd (19 August 1923 – 18 April 2003) was an English computer scientist who, while working for IBM, invented the relational model for database management, the theoretical basis for relational databases and relational databa ...
worked at IBM in
San Jose, California
San Jose, officially San José (; ; ), is a major city in the U.S. state of California that is the cultural, financial, and political center of Silicon Valley and largest city in Northern California by both population and area. With a 2020 popul ...
, in one of their offshoot offices that were primarily involved in the development of
hard disk
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...
systems. He was unhappy with the navigational model of the CODASYL approach, notably the lack of a "search" facility. In 1970, he wrote a number of papers that outlined a new approach to database construction that eventually culminated in the groundbreaking ''A Relational Model of Data for Large Shared Data Banks''.
In this paper, he described a new system for storing and working with large databases. Instead of records being stored in some sort of
linked list
In computer science, a linked list is a linear collection of data elements whose order is not given by their physical placement in memory. Instead, each element points to the next. It is a data structure consisting of a collection of nodes whic ...
of free-form records as in CODASYL, Codd's idea was to organize the data as a number of "
tables
Table may refer to:
* Table (furniture), a piece of furniture with a flat surface and one or more legs
* Table (landform), a flat area of land
* Table (information), a data arrangement with rows and columns
* Table (database), how the table data ...
", each table being used for a different type of entity. Each table would contain a fixed number of columns containing the attributes of the entity. One or more columns of each table were designated as a
primary key
In the relational model of databases, a primary key is a ''specific choice'' of a ''minimal'' set of attributes (Column (database), columns) that uniquely specify a tuple (Row (database), row) in a Relation (database), relation (Table (database), t ...
by which the rows of the table could be uniquely identified; cross-references between tables always used these primary keys, rather than disk addresses, and queries would join tables based on these key relationships, using a set of operations based on the mathematical system of
relational calculus
The relational calculus consists of two calculi, the tuple relational calculus and the domain relational calculus, that are part of the relational model for databases and provide a declarative way to specify database queries. The raison d'être ...
(from which the model takes its name). Splitting the data into a set of normalized tables (or ''relations'') aimed to ensure that each "fact" was only stored once, thus simplifying update operations. Virtual tables called ''views'' could present the data in different ways for different users, but views could not be directly updated.
Codd used mathematical terms to define the model: relations, tuples, and domains rather than tables, rows, and columns. The terminology that is now familiar came from early implementations. Codd would later criticize the tendency for practical implementations to depart from the mathematical foundations on which the model was based.
![Relational key SVG](https://upload.wikimedia.org/wikipedia/commons/4/4c/Relational_key_SVG.svg)
The use of primary keys (user-oriented identifiers) to represent cross-table relationships, rather than disk addresses, had two primary motivations. From an engineering perspective, it enabled tables to be relocated and resized without expensive database reorganization. But Codd was more interested in the difference in semantics: the use of explicit identifiers made it easier to define update operations with clean mathematical definitions, and it also enabled query operations to be defined in terms of the established discipline of
first-order predicate calculus
First-order logic—also known as predicate logic, quantificational logic, and first-order predicate calculus—is a collection of formal systems used in mathematics, philosophy, linguistics, and computer science. First-order logic uses quan ...
; because these operations have clean mathematical properties, it becomes possible to rewrite queries in provably correct ways, which is the basis of query optimization. There is no loss of expressiveness compared with the hierarchic or network models, though the connections between tables are no longer so explicit.
In the hierarchic and network models, records were allowed to have a complex internal structure. For example, the salary history of an employee might be represented as a "repeating group" within the employee record. In the relational model, the process of normalization led to such internal structures being replaced by data held in multiple tables, connected only by logical keys.
For instance, a common use of a database system is to track information about users, their name, login information, various addresses and phone numbers. In the navigational approach, all of this data would be placed in a single variable-length record. In the relational approach, the data would be ''normalized'' into a user table, an address table and a phone number table (for instance). Records would be created in these optional tables only if the address or phone numbers were actually provided.
As well as identifying rows/records using logical identifiers rather than disk addresses, Codd changed the way in which applications assembled data from multiple records. Rather than requiring applications to gather data one record at a time by navigating the links, they would use a declarative query language that expressed what data was required, rather than the access path by which it should be found. Finding an efficient access path to the data became the responsibility of the database management system, rather than the application programmer. This process, called query optimization, depended on the fact that queries were expressed in terms of mathematical logic.
Codd's paper was picked up by two people at Berkeley, Eugene Wong and
Michael Stonebraker
Michael Ralph Stonebraker (born October 11, 1943) is a computer scientist specializing in database systems. Through a series of academic prototypes and commercial startups, Stonebraker's research and products are central to many relational databa ...
. They started a project known as
INGRES
Jean-Auguste-Dominique Ingres ( , ; 29 August 1780 – 14 January 1867) was a French Neoclassicism, Neoclassical Painting, painter. Ingres was profoundly influenced by past artistic traditions and aspired to become the guardian of academic ...
using funding that had already been allocated for a geographical database project and student programmers to produce code. Beginning in 1973, INGRES delivered its first test products which were generally ready for widespread use in 1979. INGRES was similar to
System R in a number of ways, including the use of a "language" for
data access
Data access is a generic term referring to a process which has both an IT-specific meaning and other connotations involving access rights in a broader legal and/or political sense. In the former it typically refers to software and activities relat ...
, known as
QUEL. Over time, INGRES moved to the emerging SQL standard.
IBM itself did one test implementation of the relational model,
PRTV PRTV (''Peterlee Relational Test Vehicle'') was the world's first relational database management system that could handle significant data volumes.
It was a relational query system with powerful query facilities, but very limited update facility a ...
, and a production one,
Business System 12, both now discontinued.
Honeywell
Honeywell International Inc. is an American publicly traded, multinational conglomerate corporation headquartered in Charlotte, North Carolina. It primarily operates in four areas of business: aerospace, building technologies, performance ma ...
wrote
MRDS for
Multics
Multics ("Multiplexed Information and Computing Service") is an influential early time-sharing operating system based on the concept of a single-level memory.Dennis M. Ritchie, "The Evolution of the Unix Time-sharing System", Communications of t ...
, and now there are two new implementations:
Alphora Dataphor and
Rel Rel or REL may mean:
__NOTOC__ Science and technology
* REL, a human gene
* the rel descriptor of stereochemistry, see Relative configuration
*REL (''Rassemblement Européen pour la Liberté''), European Rally for Liberty, a defunct French far-ri ...
. Most other DBMS implementations usually called ''relational'' are actually SQL DBMSs.
In 1970, the University of Michigan began development of the
MICRO Information Management System based on
D.L. Childs' Set-Theoretic Data model. MICRO was used to manage very large data sets by the
US Department of Labor
The United States Department of Labor (DOL) is one of the executive departments of the U.S. federal government. It is responsible for the administration of federal laws governing occupational safety and health, wage and hour standards, unemploym ...
, the
U.S. Environmental Protection Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
, and researchers from the
University of Alberta
The University of Alberta, also known as U of A or UAlberta, is a public research university located in Edmonton, Alberta, Canada. It was founded in 1908 by Alexander Cameron Rutherford,"A Gentleman of Strathcona – Alexander Cameron Rutherfor ...
, the
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
, and
Wayne State University
Wayne State University (WSU) is a public research university in Detroit, Michigan. It is Michigan's third-largest university. Founded in 1868, Wayne State consists of 13 schools and colleges offering approximately 350 programs to nearly 25,000 ...
. It ran on IBM mainframe computers using the
Michigan Terminal System
The Michigan Terminal System (MTS) is one of the first time-sharing computer operating systems.. Developed in 1967 at the University of Michigan for use on IBM S/360-67, S/370 and compatible mainframe computers, it was developed and used by a cons ...
.
The system remained in production until 1998.
Integrated approach
In the 1970s and 1980s, attempts were made to build database systems with integrated hardware and software. The underlying philosophy was that such integration would provide higher performance at a lower cost. Examples were
IBM System/38
The System/38 is a discontinued minicomputer and midrange computer manufactured and sold by
IBM. The system was announced in 1978. The System/38 has 48-bit addressing, which was unique for the time, and a novel integrated database system. It w ...
, the early offering of
Teradata
Teradata Corporation is an American software company that provides cloud database and analytics-related software, products, and services. The company was formed in 1979 in Brentwood, California, as a collaboration between researchers at Caltech a ...
, and the
Britton Lee, Inc.
Britton Lee Inc. was a pioneering relational database company. Renamed ShareBase, it was acquired by Teradata in June, 1990.
History
Britton Lee was founded in 1979 by David L. Britton, Geoffrey M. Lee and a group of hardware engineers along with ...
database machine.
Another approach to hardware support for database management was
ICL's
CAFS accelerator, a hardware disk controller with programmable search capabilities. In the long term, these efforts were generally unsuccessful because specialized database machines could not keep pace with the rapid development and progress of general-purpose computers. Thus most database systems nowadays are software systems running on general-purpose hardware, using general-purpose computer data storage. However, this idea is still pursued in certain applications by some companies like
Netezza
IBM Netezza (pronounced ne-teez-a) is a subsidiary of American technology company IBM that designs and markets high-performance data warehouse appliances and advanced analytics applications for uses including enterprise data warehousing, busines ...
and Oracle (
Exadata
The Oracle Exadata Database Machine (Exadata) is a computing platform optimized for running Oracle Databases.
Exadata is a combined hardware and software platform that includes scale-out Intel x86-64 compute and storage servers, RoCE or Infini ...
).
Late 1970s, SQL DBMS
IBM started working on a prototype system loosely based on Codd's concepts as ''
System R'' in the early 1970s. The first version was ready in 1974/5, and work then started on multi-table systems in which the data could be split so that all of the data for a record (some of which is optional) did not have to be stored in a single large "chunk". Subsequent multi-user versions were tested by customers in 1978 and 1979, by which time a standardized
query language
Query languages, data query languages or database query languages (DQL) are computer languages used to make queries in databases and information systems. A well known example is the Structured Query Language (SQL).
Types
Broadly, query language ...
– SQL – had been added. Codd's ideas were establishing themselves as both workable and superior to CODASYL, pushing IBM to develop a true production version of System R, known as ''SQL/DS'', and, later, ''Database 2'' (
IBM Db2
Db2 is a family of data management products, including database servers, developed by IBM. It initially supported the relational model, but was extended to support object–relational features and non-relational structures like JSON a ...
).
Larry Ellison
Lawrence Joseph Ellison (born August 17, 1944) is an American business magnate and investor who is the co-founder, executive chairman, chief technology officer (CTO) and former chief executive officer (CEO) of the American computer technology ...
's Oracle Database (or more simply,
Oracle
An oracle is a person or agency considered to provide wise and insightful counsel or prophetic predictions, most notably including precognition of the future, inspired by deities. As such, it is a form of divination.
Description
The word '' ...
) started from a different chain, based on IBM's papers on System R. Though Oracle V1 implementations were completed in 1978, it wasn't until Oracle Version 2 when Ellison beat IBM to market in 1979.
Stonebraker went on to apply the lessons from INGRES to develop a new database, Postgres, which is now known as
PostgreSQL
PostgreSQL (, ), also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to its origins as a successor to the In ...
. PostgreSQL is often used for global mission-critical applications (the .org and .info domain name registries use it as their primary
data store
In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...
, as do many large companies and financial institutions).
In Sweden, Codd's paper was also read and
Mimer SQL
Mimer SQL is an SQL-based relational database management system produced by the Swedish company ''Mimer Information Technology AB'' (Mimer AB), formerly known as ''Upright Database Technology AB''. It was originally developed as a research proje ...
was developed in the mid-1970s at
Uppsala University
Uppsala University ( sv, Uppsala universitet) is a public university, public research university in Uppsala, Sweden. Founded in 1477, it is the List of universities in Sweden, oldest university in Sweden and the Nordic countries still in opera ...
. In 1984, this project was consolidated into an independent enterprise.
Another data model, the
entity–relationship model
An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can ex ...
, emerged in 1976 and gained popularity for
database design
Database design is the organization of data according to a database model. The designer determines what data must be stored and how the data elements interrelate. With this information, they can begin to fit the data to the database model.Teorey, ...
as it emphasized a more familiar description than the earlier relational model. Later on, entity–relationship constructs were retrofitted as a
data modeling
Data modeling in software engineering is the process of creating a data model for an information system by applying certain formal techniques.
Overview
Data modeling is a process used to define and analyze data requirements needed to suppo ...
construct for the relational model, and the difference between the two has become irrelevant.
1980s, on the desktop
The 1980s ushered in the age of
desktop computing
A desktop traditionally refers to:
* The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor)
Desktop may refer to various compu ...
. The new computers empowered their users with spreadsheets like
Lotus 1-2-3
Lotus 1-2-3 is a discontinued spreadsheet program from Lotus Software (later part of IBM). It was the first killer application of the IBM PC, was hugely popular in the 1980s, and significantly contributed to the success of IBM PC-compatibles i ...
and database software like
dBASE
dBase (also stylized dBASE) was one of the first database management systems for microcomputers and the most successful in its day. The dBase system includes the core database engine, a query system, a forms engine, and a programming language ...
. The dBASE product was lightweight and easy for any computer user to understand out of the box.
C. Wayne Ratliff, the creator of dBASE, stated: "dBASE was different from programs like BASIC, C, FORTRAN, and COBOL in that a lot of the dirty work had already been done. The data manipulation is done by dBASE instead of by the user, so the user can concentrate on what he is doing, rather than having to mess with the dirty details of opening, reading, and closing files, and managing space allocation." dBASE was one of the top selling software titles in the 1980s and early 1990s.
1990s, object-oriented
The 1990s, along with a rise in
object-oriented programming
Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of pr ...
, saw a growth in how data in various databases were handled. Programmers and designers began to treat the data in their databases as
objects
Object may refer to:
General meanings
* Object (philosophy), a thing, being, or concept
** Object (abstract), an object which does not exist at any particular time or place
** Physical object, an identifiable collection of matter
* Goal, an ...
. That is to say that if a person's data were in a database, that person's attributes, such as their address, phone number, and age, were now considered to belong to that person instead of being extraneous data. This allows for relations between data to be related to objects and their
attributes
Attribute may refer to:
* Attribute (philosophy), an extrinsic property of an object
* Attribute (research), a characteristic of an object
* Grammatical modifier, in natural languages
* Attribute (computing), a specification that defines a proper ...
and not to individual fields. The term "
object–relational impedance mismatch
The object–relational impedance mismatch is a set of conceptual and technical difficulties that are often encountered when a relational database management system (RDBMS) is being served by an application program (or multiple application progra ...
" described the inconvenience of translating between programmed objects and database tables.
Object database
An object database or object-oriented database is a database management system in which information is represented in the form of objects as used in object-oriented programming. Object databases are different from relational databases which ar ...
s and
object–relational database
An object–relational database (ORD), or object–relational database management system (ORDBMS), is a database management system (DBMS) similar to a relational database, but with an object-oriented database model: objects, classes and inheritan ...
s attempt to solve this problem by providing an object-oriented language (sometimes as extensions to SQL) that programmers can use as alternative to purely relational SQL. On the programming side, libraries known as
object–relational mapping
Object–relational mapping (ORM, O/RM, and O/R mapping tool) in computer science is a programming technique for converting data between type systems using object-oriented programming languages. This creates, in effect, a "virtual object databa ...
s (ORMs) attempt to solve the same problem.
2000s, NoSQL and NewSQL
XML databases
An XML database is a data persistence software system that allows data to be specified, and sometimes stored, in XML format. This data can be queried, transformed, exported and returned to a calling system. XML databases are a flavor of document- ...
are a type of structured document-oriented database that allows querying based on
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
document attributes. XML databases are mostly used in applications where the data is conveniently viewed as a collection of documents, with a structure that can vary from the very flexible to the highly rigid: examples include scientific articles, patents, tax filings, and personnel records.
NoSQL
A NoSQL (originally referring to "non- SQL" or "non-relational") database provides a mechanism for storage and retrieval of data that is modeled in means other than the tabular relations used in relational databases. Such databases have existed ...
databases are often very fast, do not require fixed table schemas, avoid join operations by storing
denormalized data, and are designed to
scale horizontally.
In recent years, there has been a strong demand for massively distributed databases with high partition tolerance, but according to the
CAP theorem
In theoretical computer science, the CAP theorem, also named Brewer's theorem after computer scientist Eric Brewer, states that any distributed data store can provide only two of the following three guarantees:Seth Gilbert and Nancy Lynch"Brewer' ...
, it is impossible for a
distributed system
A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer sci ...
to simultaneously provide
consistency
In classical deductive logic, a consistent theory is one that does not lead to a logical contradiction. The lack of contradiction can be defined in either semantic or syntactic terms. The semantic definition states that a theory is consistent ...
, availability, and partition tolerance guarantees. A distributed system can satisfy any two of these guarantees at the same time, but not all three. For that reason, many NoSQL databases are using what is called
eventual consistency
Eventual consistency is a consistency model used in distributed computing to achieve high availability that informally guarantees that, if no new updates are made to a given data item, eventually all accesses to that item will return the last upd ...
to provide both availability and partition tolerance guarantees with a reduced level of data consistency.
NewSQL
NewSQL is a class of relational database management systems that seek to provide the scalability of NoSQL systems for online transaction processing (OLTP) workloads while maintaining the ACID guarantees of a traditional database system.
Many e ...
is a class of modern relational databases that aims to provide the same scalable performance of NoSQL systems for online transaction processing (read-write) workloads while still using SQL and maintaining the
ACID
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
guarantees of a traditional database system.
Use cases
Databases are used to support internal operations of organizations and to underpin online interactions with customers and suppliers (see
Enterprise software
Enterprise software, also known as enterprise application software (EAS), is computer software used to satisfy the needs of an organization rather than individual users. Such organizations include businesses, schools, interest-based user groups, ...
).
Databases are used to hold administrative information and more specialized data, such as engineering data or economic models. Examples include computerized
library
A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...
systems,
flight reservation systems, computerized
parts inventory system
Inventory control or stock control can be broadly defined as "the activity of checking a shop's stock". It is the process of ensuring that the right amount of supply is available within a business. However, a more focused definition takes into acco ...
s, and many
content management system
A content management system (CMS) is computer software used to manage the creation and modification of digital content (content management).''Managing Enterprise Content: A Unified Content Strategy''. Ann Rockley, Pamela Kostur, Steve Manning. New ...
s that store
website
A website (also written as a web site) is a collection of web pages and related content that is identified by a common domain name and published on at least one web server. Examples of notable websites are Google Search, Google, Facebook, Amaz ...
s as collections of webpages in a database.
Classification
One way to classify databases involves the type of their contents, for example:
bibliographic
Bibliography (from and ), as a discipline, is traditionally the academic study of books as physical, cultural objects; in this sense, it is also known as bibliology (from ). English author and bibliographer John Carter describes ''bibliography ...
, document-text, statistical, or multimedia objects. Another way is by their application area, for example: accounting, music compositions, movies, banking, manufacturing, or insurance. A third way is by some technical aspect, such as the database structure or interface type. This section lists a few of the adjectives used to characterize different kinds of databases.
* An
in-memory database
An in-memory database (IMDB, or main memory database system (MMDB) or memory resident database) is a database management system that primarily relies on main memory for computer data storage. It is contrasted with database management systems that e ...
is a database that primarily resides in
main memory
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
The central processing unit (CPU) of a computer ...
, but is typically backed-up by non-volatile computer data storage. Main memory databases are faster than disk databases, and so are often used where response time is critical, such as in telecommunications network equipment.
* An
active database
An active database is a database that includes an event-driven architecture (often in the form of ECA rules) which can respond to conditions both inside and outside the database. Possible uses include security monitoring, alerting, statistics gat ...
includes an event-driven architecture which can respond to conditions both inside and outside the database. Possible uses include security monitoring, alerting, statistics gathering and authorization. Many databases provide active database features in the form of
database trigger A database trigger is procedural code that is automatically executed in response to certain events on a particular table or view in a database. The trigger is mostly used for maintaining the integrity of the information on the database. For example ...
s.
* A
cloud database
A cloud database is a database that typically runs on a cloud computing platform and access to the database is provided as-a-service. There are two common deployment models: users can run databases on the cloud independently, using a virtual machin ...
relies on
cloud technology
Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mul ...
. Both the database and most of its DBMS reside remotely, "in the cloud", while its applications are both developed by programmers and later maintained and used by end-users through a
web browser
A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on ...
and
Open API
An open API (often referred to as a public API) is a publicly available application programming interface that provides developers with programmatic access to a proprietary software application or web service. APIs are sets of requirements that g ...
s.
*
Data warehouse
In computing, a data warehouse (DW or DWH), also known as an enterprise data warehouse (EDW), is a system used for Business reporting, reporting and data analysis and is considered a core component of business intelligence. DWs are central Repos ...
s archive data from operational databases and often from external sources such as market research firms. The warehouse becomes the central source of data for use by managers and other end-users who may not have access to operational data. For example, sales data might be aggregated to weekly totals and converted from internal product codes to use
UPCs so that they can be compared with
ACNielsen
The Nielsen Corporation, self-referentially known as The Nielsen Company, and formerly known as ACNielsen or AC Nielsen, is a global marketing research firm, with worldwide headquarters in New York City, United States. Regional headquarters for ...
data. Some basic and essential components of data warehousing include extracting, analyzing, and
mining
Mining is the extraction of valuable minerals or other geological materials from the Earth, usually from an ore body, lode, vein, seam, reef, or placer deposit. The exploitation of these deposits for raw material is based on the economic via ...
data, transforming, loading, and managing data so as to make them available for further use.
* A
deductive database
A deductive database is a database system that can make deductions (i.e. conclude additional facts) based on rules and facts stored in the (deductive) database. Datalog is the language typically used to specify facts, rules and queries in deducti ...
combines
logic programming
Logic programming is a programming paradigm which is largely based on formal logic. Any program written in a logic programming language is a set of sentences in logical form, expressing facts and rules about some problem domain. Major logic prog ...
with a relational database.
* A
distributed database
A distributed database is a database in which data is stored across different physical locations. It may be stored in multiple computers located in the same physical location (e.g. a data centre); or maybe dispersed over a network of interconnect ...
is one in which both the data and the DBMS span multiple computers.
* A
document-oriented database
A document-oriented database, or document store, is a computer program and data storage system designed for storing, retrieving and managing document-oriented information, also known as semi-structured data.
Document-oriented databases are one ...
is designed for storing, retrieving, and managing document-oriented, or semi structured, information. Document-oriented databases are one of the main categories of NoSQL databases.
* An
embedded database
An embedded database system is a database management system (DBMS) which is tightly integrated with an application software; it is embedded in the application. It is a broad technology category that includes:
* database systems with differing ...
system is a DBMS which is tightly integrated with an application software that requires access to stored data in such a way that the DBMS is hidden from the application's end-users and requires little or no ongoing maintenance.
*End-user databases consist of data developed by individual end-users. Examples of these are collections of documents, spreadsheets, presentations, multimedia, and other files. Several products exist to support such databases. Some of them are much simpler than full-fledged DBMSs, with more elementary DBMS functionality.
* A
federated database system A federated database system (FDBS) is a type of meta-database management system (DBMS), which transparently maps multiple autonomous database systems into a single federated database. The constituent databases are interconnected via a computer netwo ...
comprises several distinct databases, each with its own DBMS. It is handled as a single database by a federated database management system (FDBMS), which transparently integrates multiple autonomous DBMSs, possibly of different types (in which case it would also be a
heterogeneous database system A heterogeneous database system is an automated (or semi-automated) system for the integration of heterogeneous, disparate database management systems to present a user with a single, unified query interface.
Heterogeneous database systems (HDBs) ...
), and provides them with an integrated conceptual view.
* Sometimes the term ''multi-database'' is used as a synonym for federated database, though it may refer to a less integrated (e.g., without an FDBMS and a managed integrated schema) group of databases that cooperate in a single application. In this case, typically
middleware
Middleware is a type of computer software that provides services to software applications beyond those available from the operating system. It can be described as "software glue".
Middleware makes it easier for software developers to implement co ...
is used for distribution, which typically includes an atomic commit protocol (ACP), e.g., the
two-phase commit protocol
In transaction processing, databases, and computer networking, the two-phase commit protocol (2PC) is a type of atomic commitment protocol (ACP). It is a distributed algorithm that coordinates all the processes that participate in a distributed a ...
, to allow
distributed (global) transactions across the participating databases.
* A
graph database
A graph database (GDB) is a database that uses graph structures for semantic queries with nodes, edges, and properties to represent and store data. A key concept of the system is the ''graph'' (or ''edge'' or ''relationship''). The graph relat ...
is a kind of NoSQL database that uses
graph structures with nodes, edges, and properties to represent and store information. General graph databases that can store any graph are distinct from specialized graph databases such as
triplestore
A triplestore or RDF store is a purpose-built database for the storage and retrieval of triples through semantic queries. A triple is a data entity composed of subject–predicate–object, like "Bob is 35" or "Bob knows Fred".
Much like a relati ...
s and
network databases.
* An
array DBMS
Array database management systems (array DBMSs) provide database services specifically for arrays (also called raster data), that is: homogeneous collections of data items (often called pixels, voxels, etc.), sitting on a regular grid of one, two, ...
is a kind of NoSQL DBMS that allows modeling, storage, and retrieval of (usually large) multi-dimensional
arrays
An array is a systematic arrangement of similar objects, usually in rows and columns.
Things called an array include:
{{TOC right
Music
* In twelve-tone and serial composition, the presentation of simultaneous twelve-tone sets such that the ...
such as satellite images and climate simulation output.
* In a
hypertext
Hypertext is E-text, text displayed on a computer display or other electronic devices with references (hyperlinks) to other text that the reader can immediately access. Hypertext documents are interconnected by hyperlinks, which are typi ...
or
hypermedia
Hypermedia, an extension of the term hypertext, is a nonlinear medium of information that includes graphics, audio, video, plain text and hyperlinks. This designation contrasts with the broader term ''multimedia'', which may include non-interac ...
database, any word or a piece of text representing an object, e.g., another piece of text, an article, a picture, or a film, can be
hyperlink
In computing, a hyperlink, or simply a link, is a digital reference to data that the user can follow or be guided by clicking or tapping. A hyperlink points to a whole document or to a specific element within a document. Hypertext is text wit ...
ed to that object. Hypertext databases are particularly useful for organizing large amounts of disparate information. For example, they are useful for organizing online encyclopedias, where users can conveniently jump around the text. The World Wide Web is thus a large distributed hypertext database.
* A knowledge base (abbreviated KB, kb or Δ) is a special kind of database for knowledge management, providing the means for the computerized collection, organization, and Information retrieval, retrieval of knowledge. Also a collection of data representing problems with their solutions and related experiences.
* A mobile database can be carried on or synchronized from a mobile computing device.
* Operational databases store detailed data about the operations of an organization. They typically process relatively high volumes of updates using transaction (database), transactions. Examples include Customer relationship management, customer databases that record contact, credit, and demographic information about a business's customers, personnel databases that hold information such as salary, benefits, skills data about employees, enterprise resource planning systems that record details about product components, parts inventory, and financial databases that keep track of the organization's money, accounting and financial dealings.
* A parallel database seeks to improve performance through Parallel computing, parallelization for tasks such as loading data, building indexes and evaluating queries.
::The major parallel DBMS architectures which are induced by the underlying Computer hardware, hardware architecture are:
::* Shared memory architecture, where multiple processors share the main memory space, as well as other data storage.
::* Shared disk architecture, where each processing unit (typically consisting of multiple processors) has its own main memory, but all units share the other storage.
::* Shared-nothing architecture, where each processing unit has its own main memory and other storage.
* Probabilistic databases employ fuzzy logic to draw inferences from imprecise data.
* Real-time databases process transactions fast enough for the result to come back and be acted on right away.
* A spatial database can store the data with multidimensional features. The queries on such data include location-based queries, like "Where is the closest hotel in my area?".
* A temporal database has built-in time aspects, for example a temporal data model and a temporal version of
SQL. More specifically the temporal aspects usually include valid-time and transaction-time.
* A terminology-oriented database builds upon an object-oriented database, often customized for a specific field.
* An unstructured data database is intended to store in a manageable and protected way diverse objects that do not fit naturally and conveniently in common databases. It may include email messages, documents, journals, multimedia objects, etc. The name may be misleading since some objects can be highly structured. However, the entire possible object collection does not fit into a predefined structured framework. Most established DBMSs now support unstructured data in various ways, and new dedicated DBMSs are emerging.
Database management system
Connolly and Begg define database management system (DBMS) as a "software system that enables users to define, create, maintain and control access to the database". Examples of DBMS's include
MySQL
MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database o ...
, MariaDB,
PostgreSQL
PostgreSQL (, ), also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL compliance. It was originally named POSTGRES, referring to its origins as a successor to the In ...
,
Microsoft SQL Server
Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ma ...
, Oracle Database, and Microsoft Access.
The DBMS acronym is sometimes extended to indicate the underlying
database model
A database model is a type of data model that determines the logical structure of a database. It fundamentally determines in which manner data can be stored, organized and manipulated. The most popular example of a database model is the relational ...
, with RDBMS for the Relational model, relational, OODBMS for the Object model, object (oriented) and ORDBMS for the object–relational_database, object–relational model. Other extensions can indicate some other characteristics, such as DDBMS for a distributed database management systems.
The functionality provided by a DBMS can vary enormously. The core functionality is the storage, retrieval and update of data. Edgar F. Codd, Codd proposed the following functions and services a fully-fledged general purpose DBMS should provide:
* Data storage, retrieval and update
* User accessible catalog or data dictionary describing the metadata
* Support for transactions and concurrency
* Facilities for recovering the database should it become damaged
* Support for authorization of access and update of data
* Access support from remote locations
* Enforcing constraints to ensure data in the database abides by certain rules
It is also generally to be expected the DBMS will provide a set of utilities for such purposes as may be necessary to administer the database effectively, including import, export, monitoring, defragmentation and analysis utilities. The core part of the DBMS interacting between the database and the application interface sometimes referred to as the database engine.
Often DBMSs will have configuration parameters that can be statically and dynamically tuned, for example the maximum amount of main memory on a server the database can use. The trend is to minimize the amount of manual configuration, and for cases such as
embedded database
An embedded database system is a database management system (DBMS) which is tightly integrated with an application software; it is embedded in the application. It is a broad technology category that includes:
* database systems with differing ...
s the need to target zero-administration is paramount.
The large major enterprise DBMSs have tended to increase in size and functionality and have involved up to thousands of human years of development effort throughout their lifetime.
Early multi-user DBMS typically only allowed for the application to reside on the same computer with access via Computer terminal, terminals or terminal emulation software. The client–server architecture was a development where the application resided on a client desktop and the database on a server allowing the processing to be distributed. This evolved into a multitier architecture incorporating application servers and web servers with the end user interface via a
web browser
A web browser is application software for accessing websites. When a user requests a web page from a particular website, the browser retrieves its files from a web server and then displays the page on the user's screen. Browsers are used on ...
with the database only directly connected to the adjacent tier.
A general-purpose DBMS will provide public application programming interfaces (API) and optionally a processor for database languages such as
SQL to allow applications to be written to interact with and manipulate the database. A special purpose DBMS may use a private API and be specifically customized and linked to a single application. For example, an email system performs many of the functions of a general-purpose DBMS such as message insertion, message deletion, attachment handling, blocklist lookup, associating messages an email address and so forth however these functions are limited to what is required to handle email.
Application
External interaction with the database will be via an application program that interfaces with the DBMS. This can range from a Comparison of database tools, database tool that allows users to execute SQL queries textually or graphically, to a website that happens to use a database to store and search information.
Application program interface
A programmer will Computer programming, code interactions to the database (sometimes referred to as a datasource) via an application program interface (API) or via a #database language, database language. The particular API or language chosen will need to be supported by DBMS, possibly indirectly via a preprocessor or a bridging API. Some API's aim to be database independent, ODBC being a commonly known example. Other common API's include JDBC and ADO.NET.
Database languages
Database languages are special-purpose languages, which allow one or more of the following tasks, sometimes distinguished as sublanguages:
* Data control language (DCL) – controls access to data;
* Data definition language (DDL) – defines data types such as creating, altering, or dropping tables and the relationships among them;
* Data manipulation language (DML) – performs tasks such as inserting, updating, or deleting data occurrences;
* Data query language (DQL) – allows searching for information and computing derived information.
Database languages are specific to a particular data model. Notable examples include:
* SQL combines the roles of data definition, data manipulation, and query in a single language. It was one of the first commercial languages for the relational model, although it departs in some respects from Codd's 12 rules, the relational model as described by Codd (for example, the rows and columns of a table can be ordered). SQL became a standard of the American National Standards Institute (ANSI) in 1986, and of the International Organization for Standardization (ISO) in 1987. The standards have been regularly enhanced since and are supported (with varying degrees of conformance) by all mainstream commercial relational DBMSs.
* Object Query Language, OQL is an object model language standard (from the Object Data Management Group). It has influenced the design of some of the newer query languages like JDOQL and EJB QL.
*
XQuery
XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, bin ...
is a standard XML query language implemented by XML database systems such as MarkLogic and eXist, by relational databases with XML capability such as Oracle and Db2, and also by in-memory XML processors such as Saxon XSLT, Saxon.
* SQL/XML combines
XQuery
XQuery (XML Query) is a query and functional programming language that queries and transforms collections of structured and unstructured data, usually in the form of XML, text and with vendor-specific extensions for other data formats (JSON, bin ...
with SQL.
A database language may also incorporate features like:
* DBMS-specific configuration and storage engine management
* Computations to modify query results, like counting, summing, averaging, sorting, grouping, and cross-referencing
* Constraint enforcement (e.g. in an automotive database, only allowing one engine type per car)
* Application programming interface version of the query language, for programmer convenience
Storage
Database storage is the container of the physical materialization of a database. It comprises the ''internal'' (physical) ''level'' in the database architecture. It also contains all the information needed (e.g., metadata, "data about the data", and internal data structures) to reconstruct the ''conceptual level'' and ''external level'' from the internal level when needed. Databases as digital objects contain three layers of information which must be stored: the data, the structure, and the semantics. Proper storage of all three layers is needed for future Database preservation, preservation and longevity of the database. Putting data into permanent storage is generally the responsibility of the database engine a.k.a. "storage engine". Though typically accessed by a DBMS through the underlying operating system (and often using the operating systems'
file system
In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...
s as intermediates for storage layout), storage properties and configuration settings are extremely important for the efficient operation of the DBMS, and thus are closely maintained by database administrators. A DBMS, while in operation, always has its database residing in several types of storage (e.g., memory and external storage). The database data and the additional needed information, possibly in very large amounts, are coded into bits. Data typically reside in the storage in structures that look completely different from the way the data look at the conceptual and external levels, but in ways that attempt to optimize (the best possible) these levels' reconstruction when needed by users and programs, as well as for computing additional types of needed information from the data (e.g., when querying the database).
Some DBMSs support specifying which character encoding was used to store data, so multiple encodings can be used in the same database.
Various low-level database storage structures are used by the storage engine to serialize the data model so it can be written to the medium of choice. Techniques such as indexing may be used to improve performance. Conventional storage is row-oriented, but there are also column-oriented DBMS, column-oriented and correlation databases.
Materialized views
Often storage redundancy is employed to increase performance. A common example is storing ''materialized views'', which consist of frequently needed ''external views'' or query results. Storing such views saves the expensive computing them each time they are needed. The downsides of materialized views are the overhead incurred when updating them to keep them synchronized with their original updated database data, and the cost of storage redundancy.
Replication
Occasionally a database employs storage redundancy by database objects replication (with one or more copies) to increase data availability (both to improve performance of simultaneous multiple end-user accesses to the same database object, and to provide resiliency in a case of partial failure of a distributed database). Updates of a replicated object need to be synchronized across the object copies. In many cases, the entire database is replicated.
Virtualization
With data virtualization, the data used remains in its original locations and real-time access is established to allow analytics across multiple sources. This can aid in resolving some technical difficulties such as compatibility problems when combining data from various platforms, lowering the risk of error caused by faulty data, and guaranteeing that the newest data is used. Furthermore, avoiding the creation of a new database containing personal information can make it easier to comply with privacy regulations. However, with data virtualization, the connection to all necessary data sources must be operational as there is no local copy of the data, which is one of the main drawbacks of the approach.
Security
Database security deals with all various aspects of protecting the database content, its owners, and its users. It ranges from protection from intentional unauthorized database uses to unintentional database accesses by unauthorized entities (e.g., a person or a computer program).
Database access control deals with controlling who (a person or a certain computer program) are allowed to access what information in the database. The information may comprise specific database objects (e.g., record types, specific records, data structures), certain computations over certain objects (e.g., query types, or specific queries), or using specific access paths to the former (e.g., using specific indexes or other data structures to access information). Database access controls are set by special authorized (by the database owner) personnel that uses dedicated protected security DBMS interfaces.
This may be managed directly on an individual basis, or by the assignment of individuals and Privilege (Computing), privileges to groups, or (in the most elaborate models) through the assignment of individuals and groups to roles which are then granted entitlements. Data security prevents unauthorized users from viewing or updating the database. Using passwords, users are allowed access to the entire database or subsets of it called "subschemas". For example, an employee database can contain all the data about an individual employee, but one group of users may be authorized to view only payroll data, while others are allowed access to only work history and medical data. If the DBMS provides a way to interactively enter and update the database, as well as interrogate it, this capability allows for managing personal databases.
Data security in general deals with protecting specific chunks of data, both physically (i.e., from corruption, or destruction, or removal; e.g., see physical security), or the interpretation of them, or parts of them to meaningful information (e.g., by looking at the strings of bits that they comprise, concluding specific valid credit-card numbers; e.g., see data encryption).
Change and access logging records who accessed which attributes, what was changed, and when it was changed. Logging services allow for a forensic database audit later by keeping a record of access occurrences and changes. Sometimes application-level code is used to record changes rather than leaving this in the database. Monitoring can be set up to attempt to detect security breaches. Therefore, organizations must take database security seriously because of the many benefits it provides. Organizations will be safeguarded from security breaches and hacking activities like firewall intrusion, virus spread, and ransom ware. This helps in protecting the company’s essential information, which cannot be shared with outsiders at any cause.
Transactions and concurrency
Database transactions can be used to introduce some level of
fault tolerance
Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
and data integrity after recovery from a Crash (computing), crash. A database transaction is a unit of work, typically encapsulating a number of operations over a database (e.g., reading a database object, writing, acquiring or releasing a Lock (database), lock, etc.), an abstraction supported in database and also other systems. Each transaction has well defined boundaries in terms of which program/code executions are included in that transaction (determined by the transaction's programmer via special transaction commands).
The acronym ACID describes some ideal properties of a database transaction: Atomicity (database systems), atomicity, Consistency (database systems), consistency, Isolation (database systems), isolation, and Durability (database systems), durability.
Migration
A database built with one DBMS is not portable to another DBMS (i.e., the other DBMS cannot run it). However, in some situations, it is desirable to migrate a database from one DBMS to another. The reasons are primarily economical (different DBMSs may have different Total cost of ownership, total costs of ownership or TCOs), functional, and operational (different DBMSs may have different capabilities). The migration involves the database's transformation from one DBMS type to another. The transformation should maintain (if possible) the database related application (i.e., all related application programs) intact. Thus, the database's conceptual and external architectural levels should be maintained in the transformation. It may be desired that also some aspects of the architecture internal level are maintained. A complex or large database migration may be a complicated and costly (one-time) project by itself, which should be factored into the decision to migrate. This is in spite of the fact that tools may exist to help migration between specific DBMSs. Typically, a DBMS vendor provides tools to help import databases from other popular DBMSs.
Building, maintaining, and tuning
After designing a database for an application, the next stage is building the database. Typically, an appropriate general-purpose DBMS can be selected to be used for this purpose. A DBMS provides the needed user interfaces to be used by database administrators to define the needed application's data structures within the DBMS's respective data model. Other user interfaces are used to select needed DBMS parameters (like security related, storage allocation parameters, etc.).
When the database is ready (all its data structures and other needed components are defined), it is typically populated with initial application's data (database initialization, which is typically a distinct project; in many cases using specialized DBMS interfaces that support bulk insertion) before making it operational. In some cases, the database becomes operational while empty of application data, and data are accumulated during its operation.
After the database is created, initialized and populated it needs to be maintained. Various database parameters may need changing and the database may need to be tuned (Database tuning, tuning) for better performance; application's data structures may be changed or added, new related application programs may be written to add to the application's functionality, etc.
Backup and restore
Sometimes it is desired to bring a database back to a previous state (for many reasons, e.g., cases when the database is found corrupted due to a software error, or if it has been updated with erroneous data). To achieve this, a backup operation is done occasionally or continuously, where each desired database state (i.e., the values of its data and their embedding in database's data structures) is kept within dedicated backup files (many techniques exist to do this effectively). When it is decided by a database administrator to bring the database back to this state (e.g., by specifying this state by a desired point in time when the database was in this state), these files are used to restore that state.
Static analysis
Static analysis techniques for software verification can be applied also in the scenario of query languages. In particular, the *Abstract interpretation framework has been extended to the field of query languages for relational databases as a way to support sound approximation techniques. The semantics of query languages can be tuned according to suitable abstractions of the concrete domain of data. The abstraction of relational database systems has many interesting applications, in particular, for security purposes, such as fine-grained access control, watermarking, etc.
Miscellaneous features
Other DBMS features might include:
* Database logs – This helps in keeping a history of the executed functions.
* Graphics component for producing graphs and charts, especially in a data warehouse system.
* Query optimizer – Performs query optimization on every query to choose an efficient ''query plan'' (a partial order (tree) of operations) to be executed to compute the query result. May be specific to a particular storage engine.
* Tools or hooks for database design, application programming, application program maintenance, database performance analysis and monitoring, database configuration monitoring, DBMS hardware configuration (a DBMS and related database may span computers, networks, and storage units) and related database mapping (especially for a distributed DBMS), storage allocation and database layout monitoring, storage migration, etc.
Increasingly, there are calls for a single system that incorporates all of these core functionalities into the same build, test, and deployment framework for database management and source control. Borrowing from other developments in the software industry, some market such offerings as "DevOps for database".
Design and modeling
![Process of database design v2](https://upload.wikimedia.org/wikipedia/commons/0/09/Process_of_database_design_v2.png)
The first task of a database designer is to produce a conceptual data model that reflects the structure of the information to be held in the database. A common approach to this is to develop an
entity–relationship model
An entity–relationship model (or ER model) describes interrelated things of interest in a specific domain of knowledge. A basic ER model is composed of entity types (which classify the things of interest) and specifies relationships that can ex ...
, often with the aid of drawing tools. Another popular approach is the Unified Modeling Language. A successful data model will accurately reflect the possible state of the external world being modeled: for example, if people can have more than one phone number, it will allow this information to be captured. Designing a good conceptual data model requires a good understanding of the application domain; it typically involves asking deep questions about the things of interest to an organization, like "can a customer also be a supplier?", or "if a product is sold with two different forms of packaging, are those the same product or different products?", or "if a plane flies from New York to Dubai via Frankfurt, is that one flight or two (or maybe even three)?". The answers to these questions establish definitions of the terminology used for entities (customers, products, flights, flight segments) and their relationships and attributes.
Producing the conceptual data model sometimes involves input from Business process modeling, business processes, or the analysis of workflow in the organization. This can help to establish what information is needed in the database, and what can be left out. For example, it can help when deciding whether the database needs to hold historic data as well as current data.
Having produced a conceptual data model that users are happy with, the next stage is to translate this into a Database schema, schema that implements the relevant data structures within the database. This process is often called logical database design, and the output is a logical data model expressed in the form of a schema. Whereas the conceptual data model is (in theory at least) independent of the choice of database technology, the logical data model will be expressed in terms of a particular database model supported by the chosen DBMS. (The terms ''data model'' and ''database model'' are often used interchangeably, but in this article we use ''data model'' for the design of a specific database, and ''database model'' for the modeling notation used to express that design).
The most popular database model for general-purpose databases is the relational model, or more precisely, the relational model as represented by the SQL language. The process of creating a logical database design using this model uses a methodical approach known as Database normalization, normalization. The goal of normalization is to ensure that each elementary "fact" is only recorded in one place, so that insertions, updates, and deletions automatically maintain consistency.
The final stage of database design is to make the decisions that affect performance, scalability, recovery, security, and the like, which depend on the particular DBMS. This is often called ''physical database design'', and the output is the physical data model. A key goal during this stage is data independence, meaning that the decisions made for performance optimization purposes should be invisible to end-users and applications. There are two types of data independence: Physical data independence and logical data independence. Physical design is driven mainly by performance requirements, and requires a good knowledge of the expected workload and access patterns, and a deep understanding of the features offered by the chosen DBMS.
Another aspect of physical database design is security. It involves both defining access control to database objects as well as defining security levels and methods for the data itself.
Models
![Database models](https://upload.wikimedia.org/wikipedia/commons/3/3b/Database_models.jpg)
A database model is a type of data model that determines the logical structure of a database and fundamentally determines in which manner data can be stored, organized, and manipulated. The most popular example of a database model is the relational model (or the SQL approximation of relational), which uses a table-based format.
Common logical data models for databases include:
*Navigational databases
**Hierarchical database model
**Network model
**Graph database
*Relational model
*Entity–relationship model
**Enhanced entity–relationship model
*Object database, Object model
*Document-oriented database, Document model
*Entity–attribute–value model
*Star schema
An object–relational database combines the two related structures.
Physical data models include:
*Inverted index
*Flat file database, Flat file
Other models include:
*Multidimensional database, Multidimensional model
*Array DBMS, Array model
*Multivalue model
Specialized models are optimized for particular types of data:
*XML database
*Semantic data model, Semantic model
*Content store
*Event store
*Time series database, Time series model
External, conceptual, and internal views
A database management system provides three views of the database data:
* The external level defines how each group of end-users sees the organization of data in the database. A single database can have any number of views at the external level.
* The conceptual level (or ''logical level'') unifies the various external views into a compatible global view. It provides the synthesis of all the external views. It is out of the scope of the various database end-users, and is rather of interest to database application developers and database administrators.
* The internal level (or ''physical level'') is the internal organization of data inside a DBMS. It is concerned with cost, performance, scalability and other operational matters. It deals with storage layout of the data, using storage structures such as Index (database), indexes to enhance performance. Occasionally it stores data of individual views (materialized views), computed from generic data, if performance justification exists for such redundancy. It balances all the external views' performance requirements, possibly conflicting, in an attempt to optimize overall performance across all activities.
While there is typically only one conceptual and internal view of the data, there can be any number of different external views. This allows users to see database information in a more business-related way rather than from a technical, processing viewpoint. For example, a financial department of a company needs the payment details of all employees as part of the company's expenses, but does not need details about employees that are in the interest of the human resources department. Thus different departments need different ''views'' of the company's database.
The three-level database architecture relates to the concept of ''data independence'' which was one of the major initial driving forces of the relational model. The idea is that changes made at a certain level do not affect the view at a higher level. For example, changes in the internal level do not affect application programs written using conceptual level interfaces, which reduces the impact of making physical changes to improve performance.
The conceptual view provides a level of indirection between internal and external. On the one hand it provides a common view of the database, independent of different external view structures, and on the other hand it abstracts away details of how the data are stored or managed (internal level). In principle every level, and even every external view, can be presented by a different data model. In practice usually a given DBMS uses the same data model for both the external and the conceptual levels (e.g., relational model). The internal level, which is hidden inside the DBMS and depends on its implementation, requires a different level of detail and uses its own types of data structure types.
Research
Database technology has been an active research topic since the 1960s, both in academia and in the research and development groups of companies (for example IBM Research). Research activity includes Database theory, theory and development of prototypes. Notable research topics have included Data model, models, the atomic transaction concept, related concurrency control techniques, query languages and query optimization methods, RAID, and more.
The database research area has several dedicated academic journals (for example, ''ACM Transactions on Database Systems''-TODS, ''Data and Knowledge Engineering''-DKE) and annual Academic conference, conferences (e.g., Association for Computing Machinery, ACM SIGMOD, ACM Symposium on Principles of Database Systems, PODS, VLDB conference, VLDB, IEEE ICDE).
See also
* Comparison of database tools
* Comparison of object database management systems
* Comparison of object–relational database management systems
* Comparison of relational database management systems
* Data hierarchy
* Data bank
* Data store
* Database theory
* Database testing
* Database-centric architecture
* Flat-file database
* INP (database)
* Journal of Database Management
* Question-focused dataset
Notes
References
Sources
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Further reading
* Ling Liu and Tamer M. Özsu (Eds.) (2009).
Encyclopedia of Database Systems 4100 p. 60 illus. .
* Gray, J. and Reuter, A. ''Transaction Processing: Concepts and Techniques'', 1st edition, Morgan Kaufmann Publishers, 1992.
* Kroenke, David M. and David J. Auer. ''Database Concepts.'' 3rd ed. New York: Prentice, 2007.
* Raghu Ramakrishnan and Johannes Gehrke,
Database Management Systems'
* Abraham Silberschatz, Henry F. Korth, S. Sudarshan,
Database System Concepts'
*
* Teorey, T.; Lightstone, S. and Nadeau, T. ''Database Modeling & Design: Logical Design'', 4th edition, Morgan Kaufmann Press, 2005.
External links
DB File extensionnbsp;– information about files with the DB extension
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Databases,
Database management systems,