Database Schema

The schema (pronounced skee-ma) of a database system is its structure described in a formal language supported by the database management system (DBMS). In a relational database, the schema defines the tables, the fields, relationships, views, indexes, packages, procedures, functions, queues, triggers, types, sequences, materialized views, synonyms, database links, directories, Java, XML schemas, and other elements.

Schemas are generally stored in a data dictionary. Although a schema is defined in text database language, the term is often used to refer to a graphical depiction of the database structure. In other words, schema is the structure of the database that defines the objects in the database.
[edit] Levels of database schema

* Conceptual schema, a map of concepts and their relationships.
* Logical schema, a map of entities and their attributes and relations
* Physical schema, a particular implementation of a logical schema
* Schema object, Oracle database object

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