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We address the issues of semantics and conversations for agent communication languages and the Knowledge Query Manipulation Language (KQML) in particular. Based on ideas from speech act theory, we present a semantic description for KQML that associates \cognitive" states of the agent with the use of the language's primitives (performatives). We have used this approach to describe the semantics for the whole set of reserved KQML performatives. Building on the semantics, we devise the conversation policies, i.e., a formal description of how KQML performatives may be combined into KQML exchanges (conversations), using a De nite Clause Grammar. Our research o ers methods for a speech act theory-based semantic description of a language of communication acts and for the speci cation of the protocols associated with these acts. Languages of communication acts address the issue of communication among software applications at a level of abstraction that is useful to the emerging software agents paradigm.

We address why, and especially how, to We argue that this new approach meets the overall requirements to a greater extent than any of the previous approaches, including than KIF, the leading previous declarative approach.We have implemented both aspects of our approach; a free alpha prototype called Common-

Abstract. Non-expert users have to accomplish non-trivial tasks in application and device-rich computing environments. The increasing complexity of such environments is detrimental to user productivity (and occasionally, sanity). We propose to reduce these difficulties by shifting focus to what users want to do (i.e., on the tasks at hand) rather than on the specific means for doing those tasks. We call this shift in focus "task computing"; we argue that "task computing" offers an incentive to device manufacturers to incorporate semantic web technologies into their devices in order to get the benefits of easier and more flexible use of their devices' features by end-users. To support task computing, we developed an environment called a "Task Computing Environment" (TCE), which we have implemented using standard Semantic Web (RDF, OWL, DAML-S), Web Services (SOAP, WSDL) and pervasive computing (UPnP) technologies, we describe and evaluate our TCE implementation, and we discuss how it has been used to realize various deviceusage scenarios.

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