Compositionality of programs is an important concern in knowledge represent
ation and software development. In the context of Logic Programming, up til
l now, the issue has mostly been studied for definite programs only. Here,
we study compositionality in the context of normal open logic programming.
This is a logic for knowledge representation in the context of uncertainty
and incomplete knowledge an concepts and on problem domain, in which the co
mpositionality issue turns up very naturally. The semantics of the logic is
a generalisation (allowing non-Herbrand interpretations) of the well-found
ed semantics. We provide a number of results which offer different sufficie
nt conditions under which the models of the composition of two theories can
be related to the intersection of the models of the composing theories. In
particular, under these conditions, logical consequence will be preserved
under composition. (C) 2000 Elsevier Science Inc. All rights reserved.