We introduce [Ascr ]k, an extension of the action description language [Ascr ] (Gelfond and Lifschitz, 1993) to handle actions which affect knowledge. We use sensing actions to increase an agent's knowledge of the world and non-deterministic actions to remove knowledge. We include complex plans involving conditionals and loops in our query language for hypothetical reasoning. We also present a translation of [Ascr ]k domain descriptions into epistemic logic programs.This paper extends the results of the work first presented in Lobo et al. (1997).

We propose a general framework for first-order functional logic programming, supporting lazy functions, non-determinism and polymorphic datatypes whose data constructors obey a set [Cscr ] of equational axioms. On top of a given [Cscr ], we specify a program as a set [Rscr ] of [Cscr ]-based conditional rewriting rules for defined functions. We argue that equational logic does not supply the proper semantics for such programs. Therefore, we present an alternative logic which includes [Cscr ]-based rewriting calculi and a notion of model. We get soundness and completeness for [Cscr ]-based rewriting w.r.t. models, existence of free models for all programs, and type preservation results. As operational semantics, we develop a sound and complete procedure for goal solving, which is based on the combination of lazy narrowing with unification modulo [Cscr ]. Our framework is quite expressive for many purposes, such as solving action and change problems, or realizing the GAMMA computation model.

Significant advances have recently been made in the area of updates of logic programs, and, more generally, updates of knowledge bases and their applications. Accordingly, the journal Theory and Practice of Logic Programming has planned a special issue on Change in Knowledge Bases, tentatively scheduled to appear at the beginning of 2003.

High-quality papers are sought containing either original research results or offering an insightful synthesis of past work on various aspects of change in knowledge bases.

Revised and enhanced versions of papers published in conference proceedings that have not appeared in archival journals are eligible for submission. Surveys and comparison of state of the art techniques are also solicited.