is one of the components of the DBMS data model, which allows access to data at different levels of users allowed. Every database has exactly one physical schema and a schema concept because it only stores a set of relations, but it can have many external schema to the appropriate level for multiple audiences different uses. An external schema can have multiple views, and relationships from conceptual schema. A view can be understood as a relationship, but the record of the view is not stored in the DBMS. The view is user-defined and its results are taken from the relationships in the database (the result of the view data may be of one or more relational).
đang được dịch, vui lòng đợi..