page_title: Relational model
hierarchical_section_title: Relational model
caption_attribution_description: Relational Model for databases, highlighting the Key. The image is of two tables, one storing "login," "first name," and "last name." Another table stores "login" and "phone number." The image illustrates using a unique key to link a phone number to a first and last name. Image created Sodipodi.
context_page_description: The relational model for database management is a database model based on first-order predicate logic. Edgar F. Codd proposed it in 1969. In the relational model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is called 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. The structure in which the data is stored, and the task of responding to users' requests and retrieving the data is left to the database system, and is not visible to the user.
  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 an SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. Today, many database systems are different from the original model.
context_section_description: The relational model for database management is a database model based on first-order predicate logic. Edgar F. Codd proposed it in 1969. In the relational model of a database, all data is represented in terms of tuples, grouped into relations. A database organized in terms of the relational model is called 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. The structure in which the data is stored, and the task of responding to users' requests and retrieving the data is left to the database system, and is not visible to the user.
  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 an SQL database schema corresponds to a predicate variable; the contents of a table to a relation; key constraints, other constraints, and SQL queries correspond to predicates. Today, many database systems are different from the original model. Codd fiercely argued against deviations that compromise the original principles.
caption: In the relational model, related records are linked together with a "key".
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