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- Relation_(database) abstract "In relational database theory, a relation, as originally defined by E.F. Codd, is a set of tuples (d1, d2, ..., dn), where each element dj is a member of Dj, a data domain. Codd's original definition notwithstanding, and contrary to the usual definition in mathematics, there is no ordering to the elements of the tuples of a relation. Instead, each element is termed an attribute value. An attribute is a name paired with a domain (nowadays more commonly referred to as type or data type). An attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a set of attribute values in which no two distinct elements have the same name. Thus, in some accounts, a tuple is described as a function, mapping names to values.A set of attributes in which no two distinct elements have the same name is called a heading. A set of tuples having the same heading is called a body. A relation is thus a heading paired with a body, the heading of the relation being also the heading of each tuple in its body. The number of attributes constituting a heading is called the degree, which term also applies to tuples and relations. The term n-tuple refers to a tuple of degree n (n>=0).E. F. Codd used the term relation in its mathematical sense of a finitary relation, a set of tuples on some set of n sets S1, S2, .... ,Sn. Thus, an n-ary relation is interpreted, under the Closed World Assumption, as the extension of some n-adic predicate: all and only those n-tuples whose values, substituted for corresponding free variables in the predicate, yield propositions that hold true, appear in the relation.The term relation schema refers to a heading paired with a set of constraints defined in terms of that heading. A relation can thus be seen as an instantiation of a relation schema if it has the heading of that schema and it satisfies the applicable constraints.Sometimes a relation schema is taken to include a name. A relational database definition (database schema, sometimes referred to as a relational schema) can thus be thought of as a collection of named relation schemas.In implementations, the domain of each attribute is effectively a data type and a named relation schema is effectively a relation variable or relvar for short (see Relation Variables below).In SQL, a database language for relational databases, relations are represented by tables, where each row of a table represents a single tuple, and where the values of each attribute form a column.".
- Relation_(database) thumbnail Relational_database_terms.svg?width=300.
- Relation_(database) wikiPageID "23720058".
- Relation_(database) wikiPageRevisionID "604741078".
- Relation_(database) hasPhotoCollection Relation_(database).
- Relation_(database) subject Category:Articles_with_example_SQL_code.
- Relation_(database) subject Category:Relational_model.
- Relation_(database) comment "In relational database theory, a relation, as originally defined by E.F. Codd, is a set of tuples (d1, d2, ..., dn), where each element dj is a member of Dj, a data domain. Codd's original definition notwithstanding, and contrary to the usual definition in mathematics, there is no ordering to the elements of the tuples of a relation. Instead, each element is termed an attribute value. An attribute is a name paired with a domain (nowadays more commonly referred to as type or data type).".
- Relation_(database) label "Relation (Datenbank)".
- Relation_(database) label "Relation (database)".
- Relation_(database) label "Отношение (реляционная модель)".
- Relation_(database) label "关系 (数据库)".
- Relation_(database) label "関係 (データベース)".
- Relation_(database) sameAs Relation_(Datenbank).
- Relation_(database) sameAs 関係_(データベース).
- Relation_(database) sameAs 관계_(데이터베이스).
- Relation_(database) sameAs m.06zptxr.
- Relation_(database) sameAs Q277521.
- Relation_(database) sameAs Q277521.
- Relation_(database) wasDerivedFrom Relation_(database)?oldid=604741078.
- Relation_(database) depiction Relational_database_terms.svg.
- Relation_(database) isPrimaryTopicOf Relation_(database).
