Using Constraints for Efficient Query Processing in Nondeterministic Databases

• Authors: Kumar Vadaparty;Shamim Naqvi
• Venue: IEEE Transactions on Knowledge and Data Engineering
• Year: 1995

Nondeterministic databases store disjunctive data using OR-objects. For example, data such as 驴Part#1 is implementable using Nickel or Cobalt驴 is stored as Implement(Part#1, o1) where Dom(o1) ={Nickel, Cobalt} is the domain of the OR-object o1. A possible world of a database is obtained by replacing every OR-object by a member from its domain, and it is said to be conforming if it satisfies all the FDs (functional dependencies) associated with the database. A database D is said to fully incorporate a set ${\cal F}$ of FDs if every possible world of D is conforming. This paper studies the problem of preprocessing databases to achieve full incorporation, and also the problem of incrementally maintaining a database fully incorporated under insertions and deletions.We first define a certain property called goodness of a class ${\cal D}$ of databases for a set ${\cal F}$ of FDs; goodness can be tested efficiently and enforced easily at schema design time.For any class ${\cal D}$ of databases that is good for ${\cal F}$, we present: 1) a quadratic time algorithm for fully incorporating ${\cal F}$, 2) efficient algorithms for maintaining full incorporation under updates, and 3) lower-bounds for the algorithms of 1) and 2). Next, we show that, for classes of databases that are not good, the problem of full incorporation is, in general, coNP-complete. We also examine the complexity when OR-objects are restricted to have no more than two members, and obtain some interesting tractable algorithms, and intractability results.