Heterogeneous knowledge representation allows combination of several k
nowledge representation techniques. For instance, connectionist and sy
mbolic systems are two different computational paradigms and knowledge
representations. Unfortunately, the integration of different paradigm
s and knowledge representations is not easy and very often is informal
. In this paper, we propose a formal approach to integrate these two p
aradigms where as a symbolic system we consider a (logic) rule-based s
ystem. The integration is operated at language level between neural ne
tworks and rule languages. The formal model that allows the integratio
n is based on constraint logic programming and provides an integrated
framework to represent and process heterogeneous knowledge. In order t
o achieve this we define a new language that allows expression and mod
elling in a natural and intuitive way the above issues together with t
he operational semantics. (C) 1997 Elsevier Science B.V.