Database Schema
A Database Schema is a data model that describes a database instance.
- AKA: Physical Data Model.
- Context:
- It can be composed of one or more Data Record Schemas.
- It can be based on a Logical Data Model.
- It can be defined with a Database Definition Language.
- It can be a Canonical Database Schema.
- It can have Database Schema Objects and Database Schema Object Elements.
- It can be the Input to a Database Schema Matching System.
- It can be the Output of a Database Schema Design Task.
- It can be produced by a Data Modeler.
- …
- Example(s):
- Counter-Example(s):
- See: Schema.org, Metadata.
References
2015
- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/database_schema Retrieved:2015-5-22.
- A database schema () of a database system is its structure described in a formal language supported by the database management system (DBMS) and refers to the organization of data as a blueprint of how a database is constructed (divided into database tables in the case of Relational Databases). The formal definition of 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.
"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.
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.
In an Oracle Database system, the term "schema" has a slightly different connotation.
- A database schema () of a database system is its structure described in a formal language supported by the database management system (DBMS) and refers to the organization of data as a blueprint of how a database is constructed (divided into database tables in the case of Relational Databases). The formal definition of 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.
2009
- (Wikipedia, 2009) ⇒ http://en.wikipedia.org/wiki/Database_schema
- … 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
- … Levels of database schema