This talk takes on the task of providing a formal system of dialogue CE in which the speech acts of requesting and providing an explanation are represented as dialogue moves in the system. CE has opening rules, locution rules, dialogue rules, success rules and closing rules. The system is meant to be simple and basic, to provide a platform for developing more specialised formal dialogue systems of explanation used for specific purposes. The dialogical theory of explanation postulates that an explanation is a dialogue between two parties, one of whom asks a question requesting understanding of something which he or she claims not to understand, while the other offers a response that claims to convey the requested understanding to the party asking the question.

Traditionally, knowledge systems have operated at the intersection of a particular domain and task. The specificity of each system was key to its success - certainly in automated reasoning, but also in knowledge capture and explanation generation. My group is exploring a new class of knowledge systems (such as those required by Project Halo) that are designed to be task independent and able to answer a broad range of questions within a domain. This talk will describe our experience in building these systems, especially the challenges we have encountered in generating explanations.