Deductive Database Systems and integrity constraint checking

Today, relational database systems have been extended in several ways. One way to extend the relational database model is by adding rules. These rules can make a lot of information implicit. In other words, a lot of intensional facts Sle stored in the database through rules. Consequently, when one updates such a database, a lot of implicit updates may appear by the presence of rules. When also integrity constraints on data in the database ale allowed, the checking of these constraints becomes a problem because an update can cause some implicit updates which in turn may violate some of the constraints. The search for inconsistencies is a timeconsuming task which must therefore be done primarily at compile time. This paper presents a new method for checking integrity constraints in databases extended with rules. A special kind of database is used, namely a deductive database, which is a logical database that handles deductive rules. The goal of this paper is to find the causes of efficiency defects in existing methods. A classification of redundant evaluations in existing methods is given. On th~ basis of this analysis an improvement ofthe method based on inconsistency rules, which I have developed at an earlier stage (see [26]), is proposed. Compared to existing methods it follows a completely different approach. Inconsistency rules are meta~rules which describe for all possible updates the integrity constraint check that has to be done. Further, the check is mimimal from the redundancy types point of view. Several types of redundancy in integrity checking methods are described in this paper. These redundancies have to be avoided to provide that we only have to access a relevant part of the database that is affected by the update. The improved version of the method based on inconsistency rules is compared to other existing methods, i. e., methods based on induced update6 and methods based on potential update •. keywords: logic programming, deductive databa.e" integrity con.trainb, con6i,tency.

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