Coordination is frequently associated with shared data spaces employing Linda coordination. But in practice, communication between parallel and distributed processes is carried out with message exchange patterns. What, actually, do shared data spaces contribute beyond these? In this paper we present a formal representation for a definition of shared spaces by introducing an "extensible tuple model", based on existing research on Linda coordination, some Linda extensions, and virtual shared

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... y. The main enhancements of the extensible tuple model comprise: means for structuring of spaces, Internet-compatible addressing of resources, more powerful coordination capabilities, a clear separation of user data and coordination information, support of symmetric peer application architectures, and extensibility through programmable aspects. The advantages of the extensible tuple model (XTM) are that it allows for a specification of complex coordination patterns. We would like to thank Stefan Craß, Geri Joskowicz, Hans Moritsch, Gernot Salzer, Thomas Scheller, Vesna Sesum-Cavic, and Ralf Westphal for their helpful discussions on this topic. The project is partly funded by TripCom (IST-4-027324-STP project, http://www.tripcom.org) and CAPI (project at TU-Vienna) of the Institute of Computer Languages.