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One-to-one (data Model)
In systems analysis, a one-to-one relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model) A and B in which one element of A may only be linked to one element of B, and vice versa. In mathematical terms, there exists a bijective function from A to B. For instance, think of A as the set of all human beings, and B as the set of all their brains. Any person from A can and must have only one brain from B, and any human brain in B can and must belong to only one person that is contained in A. In a relational database, a one-to-one relationship exists when one row in a table may be linked with only one row in another table and vice versa. It is important to note that a one-to-one relationship is not a property of the data, but rather of the relationship itself. A list of mothers and their children may happen to describe mothers with only one child, in which case one row of the mothers table will refer to only one ro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Systems Analysis
Systems analysis is "the process of studying a procedure or business to identify its goal and purposes and create systems and procedures that will efficiently achieve them". Another view sees system analysis as a problem-solving technique that breaks down a system into its component pieces, and how well those parts work and interact to accomplish their purpose. The field of system analysis relates closely to requirements analysis or to operations research. It is also "an explicit formal inquiry carried out to help a decision maker identify a better course of action and make a better decision than they might otherwise have made." The terms analysis and synthesis stems from Greek, meaning "to take apart" and "to put together," respectively. These terms are used in many scientific disciplines, from mathematics and logic to economics and psychology, to denote similar investigative procedures. The analysis is defined as "the procedure by which we break down an intellectual or subst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cardinality (data Modeling)
Within data modelling, cardinality is the numerical relationship between rows of one table and rows in another. Common cardinalities include ''one-to-one'', ''one-to-many'', and ''many-to-many''. Cardinality can be used to define data models as well as analyze entities within datasets. Relationships For example, consider a database of electronic health records. Such a database could contain tables like the following: * A doctor table with information about physicians. * A patient table for medical subjects undergoing treatment. * An encounter table with an entry for each hospital visit. Natural relationships exist between these entities, such as an encounter involving many doctors. There is a many-to-many relationship between records in doctor and records in patient because doctors have many patients and patients can see many doctors. There is a one-to-many relationship between records in patient and records in encounter because patients can have many encounters and each encou ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Entity
An entity is something that exists as itself, as a subject or as an object, actually or potentially, concretely or abstractly, physically or not. It need not be of material existence. In particular, abstractions and legal fictions are usually regarded as entities. In general, there is also no presumption that an entity is animate, or present. The term is broad in scope and may refer to animals; natural features such as mountains; inanimate objects such as tables; numbers or sets as symbols written on a paper; human contrivances such as laws, corporations and academic disciplines; or supernatural beings such as gods and spirits. The adjectival form is ''entitative''. Etymology The word ''entity'' is derived from the Latin ''entitas'', which in turn derives from the Latin ''ens'' meaning "being" or "existing" (compare English ''essence''). ''Entity'' may hence literally be taken to mean "thing which exists". In philosophy Ontology is the study of concepts of existence, a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 exist between entities (instances of those entity types). In software engineering, an ER model is commonly formed to represent things a business needs to remember in order to perform business processes. Consequently, the ER model becomes an abstract data model, that defines a data or information structure which can be implemented in a database, typically a relational database. Entity–relationship modeling was developed for database and design by Peter Chen and published in a 1976 paper, with variants of the idea existing previously, but today it is commonly used for teaching students the basics of data base structure. Some ER models show super and subtype entities connected by generalization-specialization relationships, and an ER mode ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bijective
In mathematics, a bijection, also known as a bijective function, one-to-one correspondence, or invertible function, is a function between the elements of two sets, where each element of one set is paired with exactly one element of the other set, and each element of the other set is paired with exactly one element of the first set. There are no unpaired elements. In mathematical terms, a bijective function is a one-to-one (injective) and onto (surjective) mapping of a set ''X'' to a set ''Y''. The term ''one-to-one correspondence'' must not be confused with ''one-to-one function'' (an injective function; see figures). A bijection from the set ''X'' to the set ''Y'' has an inverse function from ''Y'' to ''X''. If ''X'' and ''Y'' are finite sets, then the existence of a bijection means they have the same number of elements. For infinite sets, the picture is more complicated, leading to the concept of cardinal number—a way to distinguish the various sizes of infinite sets ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 relational database systems are equipped with the option of using the SQL (Structured Query Language) for querying and maintaining the database. History The term "relational database" was first defined by E. F. Codd at IBM in 1970. Codd introduced the term in his research paper "A Relational Model of Data for Large Shared Data Banks". In this paper and later papers, he defined what he meant by "relational". One well-known definition of what constitutes a relational database system is composed of Codd's 12 rules. However, no commercial implementations of the relational model conform to all of Codd's rules, so the term has gradually come to describe a broader class of database systems, which at a minimum: # Present the data to the user as re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
One-to-many (data Model)
In systems analysis, a one-to-many relationship is a type of cardinality that refers to the relationship between two entities (see also entity–relationship model) A and B in which an element of A may be linked to many elements of B, but a member of B is linked to only one element of A. For instance, think of A as books, and B as pages. A book can have many pages, but a page can only be in one book. In a relational database, a one-to-many relationship exists when one row in table A may be linked with many rows in table B, but one row in table B is linked to only one row in table A. It is important to note that a one-to-many relationship is not a property of the data, but rather of the relationship itself. A list of authors and their books may happen to describe books with only one author, in which case one row of the books table will refer to only one row of the authors table, but the relationship itself is not one-to-many, because books ''may'' have more than one author, formi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Many-to-many (data Model)
In systems analysis, a many-to-many relationship is a type of cardinality that refers to the relationship between two entities, say, A and B, where A may contain a parent instance for which there are many children in B and vice versa. For example, think of A as Authors, and B as Books. An Author can write several Books, and a Book can be written by several Authors. In a relational database management system, such relationships are usually implemented by means of an associative table (also known as join table, junction table or ''cross-reference table''), say, AB with two one-to-many relationships A -> AB and B -> AB. In this case the logical primary key for AB is formed from the two foreign keys (i.e. copies of the primary keys of A and B). In web application frameworks such as CakePHP and Ruby on Rails, a many-to-many relationship between entity types represented by logical model database tables is sometimes referred to as a HasAndBelongsToMany (HABTM) relationship. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
