Research On The Theory Of Incomplete Information System

Incomplete information database and formal semantics of SQL are two important fields in database theory. They not only have important theoretical values, but also have great practical values. This paper investigates the theory and application of incomplete information system by using the medium logic predicate calculus system MFM. In this paper, the queries of SQL are modified and the query language to the incomplete information databases is founded. The results of SQL queries are classified into two types: sure information and maybe information. And the descriptions of SQL query are given in allusion to the different types of the answer. And the query that can deal with the incomplete information database is implemented in Linux system by using the tools of Yacc and Lex. A formal three-valued predicate calculus MFPC is constructed, which is based on the medium logic predicate calculus system MFM, and then the SQL query sentences are transformed into MFPC by syntax transforming rules. The formal semantics of SQL query is completely defined by this means. At last, the tableau system of medium logic predicate calculus system MFM is constructed, and the soundness and completeness of the system is proved. This system can act as the automated reasoning system in incomplete information environments.