Composing Open Logic Programs

Structuring logic programs to deal with evolving and incomplete knowledge is one of the main issues in representing knowledge with logic On the one hand, evolving knowledge in logic programming can be modelled through suitable operators for the dynamic composition of separate programs On the other hand, when dealing with dynamic compositions of logic programs, the open world assumption adequately models the aspects of incompleteness of knowledge We analyse the notion of open program along with suitable operators for composing and closing programs We present the semantics of open programs and of the associated operators in two different, equivalent styles We define a model-theoretic semantics in terms of Herbrand models, while an operational semantics is given by means of inference rules In the second part of the paper, we explore some applications of open programs and of their compositions We show how a number of policies for structuring logic programming can be reconstructed in this setting, including the construction of modules with import declarations. Finally, the relations between open programs and abductive logic programming are discusse