<P> The database schema of a database system is its structure 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 . </P> <P> "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 the possible end - users ." The notion of a database schema plays the same role as the notion of theory in predicate calculus . A model of this "theory" closely corresponds to a database, which can be seen at any instant of time as a mathematical object . Thus a schema can contain formulas representing integrity constraints specifically for an application and the constraints specifically for a type of database, all expressed in the same database language . In a relational database, the schema defines the tables, fields, relationships, views, indexes, packages, procedures, functions, queues, triggers, types, sequences, materialized views, synonyms, database links, directories, XML schemas, and other elements . </P>

The blueprint of any database system is the