Implementation Methods

Abstract

Chapter 23 discussed the evaluation of constraint query languages in general based on several assumptions, for example, that existential quantifier elimination and satisfiability can be implemented as functions. From a practical point of view there are many lower-level details that need to be considered for implementation of a constraint database system. In this chapter, we discuss two implementation approaches.

The first approach is a graph-based approach described in Section 24.1. This approach takes a step toward implementation by giving a graph data structure to the constraint data represented. Then it develops the algebraic operators in terms of this new data structure.

The second approach, described in Section 24.2, is a matrix-based approach that is even more concrete. In this, the graph data structure is replaced by matrices that lead to simple computer implementations. Throughout this chapter we will consider integer difference constraints as our main example. Similar graph-based or matrix-based implementation structures could be described for other types of constraints. We give just a brief outline for Boolean constraints in Section 24.3.1.