High Level Expression of Semantic Integrity Specifications in a Relational Data Base System.

摘要

The 'semantic integrity'of a data base is said to be violated when the data base ceases to represent a legitimate configuration of the application environment it is intended to model. In the context of the relational data model,it is possible to identify multiple levels of semantic integrity information: (1) the description of the domains of the data base as abstract sets of atomic data values (domain definition), (2) the specification of the fundamental structure of the relations of the data base (relation structure specification), (3) the definition of the abstract operations which are meaningful in terms of the application environment (structured operations),and (4) the expression of additional semantic information not contained in the structure of the relations nor in the identities of their underlying domains (relation constraints). A high level, nonprocedural domain definition language facilitates the description of domains. Such a language allows the specification of the properties of the values constituting a domain,and the action that is to occur if an attempt is made to update a column entry such that it does not belong to the underlying domain of that column. The specification of relation structure and structured operations can be accomplished by means of high level integrity (sub) languages. A semantic integrity subsystem (of a generalized relational data base management system) can support the generation and maintenance of integrity specifications,verify that these specifications are met by the data base,and take appropriate action if violations are detected.