Activities - Schema/subschema definition

A Schema & sub-schema form the logical view of the database.

	Schema: A named collection of files, records and fields, including relationships, and is the logical file view of the entire database. Originally used in a CODASYL network data model (1971) to describe the database, and was the comprehensive perspective.
	Subschema: Customised view of the database (Dynaset in MS-Access), which may be a partial view or in a different form. In the CODASYL database a local perspective.

Hence a database will have one schema but may have many sub-schemas.
The Database will provide facilities for creation of both Schema (File creation with relationships), and Subschemas (Dynasets). In the CODASYL model a data description language (DDL) was used to create the schema an sub-schemas.
McFadden, Hoffer (1994)