A query language allowing conditions of relational type in queries

摘要

The article deals with a certain query language of logical type, designed for use in an information system containing either complete or incomplete information. It is based on Pawlak's model of an information system. The language in question allows presentation of queries for objects with values of attributes satisfying a given k-ary relation, where k is any number not exceeding the number of attributes in the system. Expressions of the language are built up by means of Boolean operations from k-ary descriptors, representing elementary queries of the type described above. A complete system of axioms (equivalent transformation rules for queries) valid under the interpretation of the language in a complete information system is given. Based on the above axiom system, a method of computing an answer to a query of this language in an incomplete information system is described.