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Semi-structured Model
The semi-structured model is a database model where there is no separation between the data and the schema, and the amount of structure used depends on the purpose. The advantages of this model are the following: * It can represent the information of some data sources that cannot be constrained by schema. * It provides a flexible format for data exchange between different types of databases. * It can be helpful to view structured data as semi-structured (for browsing purposes). * The schema can easily be changed. * The data transfer format may be portable. The primary trade-off being made in using a semi-structured database model is that queries cannot be made as efficiently as in a more constrained structure, such as in the relational model. Typically the records in a semi-structured database are stored with unique IDs that are referenced with pointers to their location on disk. This makes navigational or path-based queries quite efficient, but for doing searches over many r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 model, which uses a table-based format. Types Common logical data models for databases include: * Hierarchical database model :It is the oldest form of data base model. It was developed by IBM for IMS (information Management System). It is a set of organized data in tree structure. DB record is a tree consisting of many groups called segments. It uses one to many relationships. The data access is also predictable. * Network model * Relational model * Entity–relationship model ** Enhanced entity–relationship model * Object model * 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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data (computing)
In computer science, data (treated as singular, plural, or as a mass noun) is any sequence of one or more symbols; datum is a single symbol of data. Data requires interpretation to become information. Digital data is data that is represented using the binary number system of ones (1) and zeros (0), instead of analog representation. In modern (post-1960) computer systems, all data is digital. Data exists in three states: data at rest, data in transit and data in use. Data within a computer, in most cases, moves as parallel data. Data moving to or from a computer, in most cases, moves as serial data. Data sourced from an analog device, such as a temperature sensor, may be converted to digital using an analog-to-digital converter. Data representing quantities, characters, or symbols on which operations are performed by a computer are stored and recorded on magnetic, optical, electronic, or mechanical recording media, and transmitted in the form of digital electrical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Database Schema
The database schema is the structure of a database described in a formal language supported by the database management system (DBMS). The term "schema" refers to the organization of data as a blueprint of how the database is constructed (divided into database tables in the case of relational databases). The formal definition of a database schema is a set of formulas (sentences) called integrity constraints imposed on a database. These integrity constraints ensure compatibility between parts of the schema. All constraints are expressible in the same language. A database can be considered a structure in realization of the database language. The states of a created conceptual schema are transformed into an explicit mapping, the database schema. This describes how real-world entities are modeled in the database. "A database schema specifies, based on the database administrator's knowledge of possible applications, the facts that can enter the database, or those of interest to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Relational Model
The relational model (RM) is an approach to managing data using a structure and language consistent with first-order predicate logic, first described in 1969 by English computer scientist Edgar F. Codd, where all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is a relational database. The purpose of the relational model is to provide a declarative method for specifying data and queries: users directly state what information the database contains and what information they want from it, and let the database management system software take care of describing data structures for storing the data and retrieval procedures for answering queries. Most relational databases use the SQL data definition and query language; these systems implement what can be regarded as an engineering approximation to the relational model. A ''table'' in a SQL database schema corresponds to a predicate variable; the contents of a tabl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Object Exchange Model
The Object Exchange Model (OEM) is a model for exchanging semi-structured data between object-oriented databases. It serves as the basic data model in numerous projects of the Stanford University Database Group, including Tsimmis, Lore, and C3. Slight variations of OEM have evolved across different Stanford projects. In Lore, labels are actually on parent-child "links" rather than objects. For example, if an OEM object has multiple parents, different parent objects may use different labels to identify that object. An atomic value encoding a person's name might be included in one complex object using the label "Author" and in another complex object using the label "Editor." In C3, additional attributes are required for each object to annotate the changes to the object that have occurred over time. OEM representationsTextua ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semi-structured Data
Semi-structured data is a form of structured data that does not obey the tabular structure of data models associated with relational databases or other forms of data tables, but nonetheless contains tags or other markers to separate semantic elements and enforce hierarchies of records and fields within the data. Therefore, it is also known as self-describing structure. In semi-structured data, the entities belonging to the same class may have different attributes even though they are grouped together, and the attributes' order is not important. Semi-structured data are increasingly occurring since the advent of the Internet where full-text documents and databases are not the only forms of data anymore, and different applications need a medium for exchanging information. In object-oriented databases, one often finds semi-structured data. Types XML XML, other markup languages, email, and EDI are all forms of semi-structured data. OEM (Object Exchange Model) was created prior ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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