Incomplete Information Database Research

Incomplete information database and SQL are two important fields in database theory,and not only have they important theoretical values,but also have great practical values. In this paper,the original extended relational model has been improved by adopting MFM in the research of incomplete information database. Though SQL has become the de facto standard of DBMS,it's well known that it has some logic flaws. In this paper,we revise and extend the SQL for incomplete information processing and get ride of the EXISTS loophole. The formal semantics of SQL is the theoritical foundation of query rewriting,but there is no satisfying method to translate SQL into a canonical form. In this paper,we propose a better formalizing method for SQL which is more succinct. Finally,we adopt this method in the design of our query rewriting component of CBase. The test result shows that the performance of CBase has been dramatically improved.