Basic Algorithms for BG Homomorphism

In this chapter, we study basic algorithms for computing one or all homomorphisms from one BG to another. We first present the basic backtrack scheme, then improve it by consistency-maintaining techniques, essentially adapted from the constraint processing domain (Sect. 6.1). As this book is about conceptual graphs and not constraint networks, these techniques are applied directly on BGs. However, another section is entirely devoted to constraint processing (Sect. 6.2), and it is intended for readers interested in further algorithmic developments. The last section deals with the problem of node label comparisons. It presents and compares data structures and associated algorithms for managing orders on types. General orders are considered, and also orders with a specific structure, e.g., trees or lattices.