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CODASYL model General information
30 U929-J-Z125-9-76
Relationships between record types and referential integrity
In figure 2, the SUPPLIES set indicates that a record of the ARTICLE record type is not an
isolated record, but is assigned to a record of the SUPPLIER record type. In UDS/SQL, it is
possible to declare in a set definition that no article may be entered without a supplier being
assigned to that article. A relationship of this type is an example of referential integrity.
Referential integrity also ensures, for example, that the relationships between order and
customer remain consistent; in this case, a customer must exist for each order. This means
that no order can be entered without the customer who placed it also being entered, and
that a given customer cannot be deleted as long as an order from that customer exists.
Language components of the CODSASYL report
The CODASYL report describes three basic language components:
1. The schema DDL (Data Description Language) defines the logical structure of the data
in the database. It allows any type of network structure to be defined.
2. The subschema DDL describes user-specific views of the database.
A subschema is a part of a schema. Two or more subschemas may exist for each
schema. These subschemas may overlap one another, i.e. a given record type may
exist in two or more subschemas. A subschema can include the entire database or
contain only a single record type.
The schema/subschema concept is a major part of data protection. Each user is
allowed to perform operations only within his or her own subschema, with no access to
the rest of the database.
3. The COBOL-DML (Data Manipulation Language) is a comprehensive language for
accessing databases. Both its range of functions and the way it is embedded in the
programming language COBOL are defined precisely. Its basic language components
are used for navigation, reading and updating in the database as well as to control
processing.