Decidability and Complexity of Simulation Preorder for Data-Centric Web Services

Abstract

In this thesis we address the problem of analyzing specifications of data-centric Web service interaction protocols (also called data-centric business protocols). Specifications of such protocols include data in addition to operation signatures and messages ordering constraints. Analysis of data-centric services is a complex task because of the inherently infinite states of the underlying service execution instances. Our work focuses on characterizing the problem of checking a refinement relation between service interaction protocol specifications. More specifically, we consider the problem of checking the simulation preorder when service business protocols are represented using data-centric state machines. First we study the Colombo model [BCG + 05]. In this framework, a service (i) exchanges messages using variables; (ii) acts on a shared database; (iii) has a transition based behavior. We show that the simulation test for unbounded Colombo is undecidable. Then, we consider the case of bounded Colombo where we show that simulation is (i) exptimecomplete for Colombo services without any access to the database (noted Colombo DB=∅), and (ii) 2exptime-complete when only bounded databases are considered (the obtained model is noted Colombo bound). In the second part of this thesis, we define a generic model to study the impact of various parameters on the simulation test in the context of datacentric services. The generic model is a guarded transition system acting (i.e., read and write) on databases (i.e., local and shared) and exchanging messages with its environment (i.e., other services or users). The model was designed with a database theory perspective, where all actions are viewed as queries (i.e modification of databases, messages exchanges and guards). In this context, we obtain the following results (i) for update free guarded services (i.e., generic services with guards and only able to send empty messages) the decidability of simulation is fully characterized w.r.t decidability of satisfiability of the query language used to express the guards augmented with a restrictive form of negation, (ii) for update free send services (i.e., generic services without guards and able to send as messages the result of queries over local and shared database), we exhibit sufficient conditions for both decidability and undecidability of simulation test w.r.t the language used to compute messages payloads, and (iii) we study the case of insert services (i.e., generic services without guards and with the ability of insert the result of queries into the local and the shared database). In this case, we study the simulation as well as the weak simulation relations where we show that: (i) the weak simulation is undecidable when the insertions are expressed as conjunctive queries, (ii) the simulation is undecidable if satisfiability of the query language used to express the insertion augmented with a restricted form of negation is undecidable. Finally, we study the interaction between the queries used as guards and the ones use...

Provenance-based analysis of data-centric processes

“…This includes datacentric business processes (e.g., [4,18]) and Web services and applications [2,22], and the analysis goals vary from verification of fully specified processes to the automatic synthesis of new processes combining a given set of components. The results obtained in these lines of research are not applicable to our needs since no provenance model was proposed there.…”

Expressive Equivalence and Succinctness of Parametrized Automata with Respect to Finite Memory Automata

“…We have shown in our previous works [2,3] how to extend the automata-based service composition approach to the case of infinite alphabets, also showing an EXPTIME solution for solving simulation preorder. Akroun et al [1] further demonstrate that it is EXPTIME-complete. However, we also provide a simpler proof of the EXPTIME-completeness claim in this paper.…”

“…Akroun et al have used such classes of automata over infinite alphabet to model verification and synthesis problems for Web Services, and give a detailed study in [1]. Parametrized automata, a class of automata introduced by the authors, is shown to be equivalent to finite memory automata with nondeterministic reassignment (NFMAs) [11] in terms of the class of languages they can represent.…”