An observational model for spatial logics

Spatiality is an important aspect of distributed systems because their computations depend both on the dynamic behaviour and on the structure of their components. Spatial logics have been proposed as the formal device for expressing spatial properties of systems. We define CCS∥, a CCS-like calculus whose semantics allows one to observe spatial aspects of systems on the top of which we define models of the spatial logic. Our alternative definition of models is proved equivalent to the standard one. Furthermore, logical equivalence is characterized in terms of the bisimilarity of CCS∥

A calculus for modeling and analyzing conversations in service-oriented computing

Dissertação apresentada para a obtenção do Grau de Doutor em Informática pela Universidade Nova de Lisboa, Faculdade de Ciências e TecnologiaThe service-oriented computing paradigm has motivated a large research effort in the past few years. On the one hand, the wide dissemination of Web-Service technology urged for the development of standards, tools and formal techniques that contributed for the design of more reliable systems. On the other hand, many of the problems presented in the study of service-oriented applications find an existing work basis in well-established research fields, as is the case of the study of interaction models that has been an active field of research in the last couple of decades. However, there are many new problems raised by the service-oriented computing paradigm in particular that call for new concepts, dedicated models and specialized formal analysis techniques. The work presented in this dissertation is inserted in such effort, with particular focus on the challenges involved in governing interaction in service-oriented applications. One of the main innovations introduced by the work presented here is the way in which multiparty interaction is handled. One reference field of research that addresses the specification and analysis of interaction of communication-centric systems is based on the notion of session. Essentially, a session characterizes the interaction between two parties, a client and a server,that exchange messages between them in a sequential and dual way. The notion of session is thus particularly adequate to model the client/server paradigm, however it fails to cope with interaction between several participants, a scenario frequently found in real service-oriented applications. The approach described in this dissertation improves on the state of the art as it allows to model and analyze systems where several parties interact, while retaining the fundamental flavor of session-based approaches, by relying on a novel notion of conversation: a simple extension of the notion of session that allows for several parties to interact in a single medium of communication in a disciplined way, via labeled message passing. The contributions of the work presented in this dissertation address the modeling and analysis of service-oriented applications in a rigorous way: First, we propose and study a formal model for service-oriented computing, the Conversation Calculus, which, building on the abstract notion of conversation, allows to capture the interactions between several parties that are relative to the same service task using a single medium of communication. Second, we introduce formal analysis techniques, namely the conversation type system and progress proof system that can be used to ensure, in a provably correct way and at static verification time (before deploying such applications), that systems enjoy good properties such as “the prescribed protocols will be followed at runtime by all conversation participants”(conversation fidelity)and “the system will never run into a stuck state” (progress). We give substantial evidence that our approach is already effective enough to model and type sophisticated service-based systems, at a fairly high level of abstraction. Examples of such systems include challenging scenarios involving simultaneous multiparty conversations, with concurrency and access to local resources, and conversations with a dynamically changing and unanticipated number of participants, that fall out of scope of previous approaches.Fundação para a Ciência e Tecnologia - PhD Scholarship SFRH/BD/23760/200

An Observational Model for Spatial Logics

Spatiality is an important aspect of distributed systems because their computations depend both on the dynamic behaviour and on the structure of their components. Spatial logics have been proposed as the formal device for expressing spatial properties of systems. We define CCS ||, a CCS-like calculus whose semantics allows one to observe spatial aspects of systems on the top of which we define models of the spatial logic. Our alternative definition of models is proved equivalent to the standard one. Furthermore, logical equivalence is characterized in terms of the bisimilarity of CCS ||.