An important issue in open agent systems such as the Internet is the discovery of service providers by potential consumers (requesters). This paper is concerned with services that involve the ongoing provision of up-to-date information to requesters. We explore three separate issues: subscription to an information provider for ongoing provision of information; monitoring for new information providers; and maintaining awareness of when providers disappear from the system. We explore several models for how this functionality may best be provided, with emphasis on the ways in which certain choices affect the overall system; and provide an analysis of preferred design options for environments with different characteristics.
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