In this paper we study the issue of service composition, for services that export a representation of their behavior in the form of a finite deterministic transition system. In particular, given a specification of the target service requested by the client as a finite deterministic transition system, the problem we face is how we can exploit the computations of the available services for realizing the computations of the target service. While ways to tackle such a problem are known, in this paper we present a new technique that is based on the notion of simulation, which is still optimal from the computational complexity point. Notably, such a technique, opens up the possibility of devising composition in a "just-in-time" fashion. Indeed, we show that, by exploiting simulation, it is actually possible to implicitly compute all possible compositions at once, and delay the choice of the actual composition to run-time.

The promise of Web Service Computing is to utilize Web services as fundamental elements for realizing distributed applications/solutions. In particular, when no available service can satisfy client request, (parts of) available services can be composed and orchestrated in order to satisfy such a request. In this paper, we address the automatic composition when component services have access control & authorization constraints, and impose further reputation constraints on other component services. In particular, access & authorization control is based on credentials, component services may (or not) trust of credentials issued by other component services and the service behavior is modeled by the possible conversations the service can have with its clients. We propose an automatic composition synthesis technique, based on reduction to satisfiability in Propositional Dynamic Logic, that is sound, complete and decidable. Moreover, we will characterize the computational complexity of the problem.

We study an

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