Logic programming for evolving agents

Logic programming has often been considered less than adequate for modelling the dynamics of knowledge changing over time. In this paper we describe Evolving Logic Programs (EVOLP), a simple though quite powerful extension of logic programming, which allows for modelling the dynamics of knowledge bases expressed by programs, and illustrate its usage in modelling agents whose specifications may dynamically change. From the syntactical point of view, evolving programs are just generalized logic programs (i.e. normal LPs plus default negation in rule heads too), extended with (possibly nested) assertions, whether in heads or bodies of rules. From the semantical point of view, a model-theoretic characterization is offered of the possible evolutions of such programs. These evolutions arise both from self (i.e. internal to the agent) updating, and from concomitant external updating originating in the environment. To illustrate the usage and power of EVOLP, and its ability to model agents' specifications, we elaborate on variations in the modelling of a Personal Assistant Agent for e-mail management.