Transactional Aspects in Coordination and Composition of Web Services (Ph.D. Thesis)
Laura Bocchi · 2006
The work presented in this thesis is positioned in the context of coordination and composition in Service Oriented Architectures and, specifically, in the Web Service Architecture. I focused on a particular coordination aspect, that is the support of transactional behavior. The classic notion of transactions, typical of database systems, evolved, granting weaker properties than the ACID ones, in order to adapt to multi-domain and loosely coupled environments. These weaker transactions, referred to as long running transactions, are object of a shared interest and are supported by most of the languages for Web service coordination and composition. Although, because the informal nature of the documents describing those languages, a common agreement has not been achieved on their actual semantics. The main contribution of my doctoral work is a formal analysis, with the pi calculus, of the emerging features of transactions in the Web Service Architecture. The choice of the pi calculus, a message-based formalism, is motivated by its suitability for the formal analysis of orchestration languages and Web transaction protocols which are also based upon message exchange in a distributed setting. Transactions are considered under two complementary perspectives. The one is the local perspective of the business process where a transaction is a control construct providing an explicit (user defined) error handling mechanism. The other, is the global perspective of transaction protocols addressing the synchronization among distributed services. According to this perspective, protocols are modeled by means of exchanges of messages among parties, analyzed and compared. Negotiation protocols have a particular relevance in this analysis. Negotiation is a well known issue in multi-agent systems, and it is a topic of interest also in the Web Service scenario because of its close relationship with the automation of the services selection. For example some proposals in the Web Service scenario, such as the cohesions in the Business Transaction Protocol, support a negotiation based on a bidding activity. vi A further contribution of my thesis consists in the investigation of the possible usage of software agents and Semantic Web techniques to enable automated service composition. Since it is crucial that also the aspects of inter-operability are compositional, aspects of inter-operability (i.e., transactional properties) are included in the service ontology to enhance automated service selection. The focus in not only on the e-business scenario but also includes e-science. The convergence of e-business and e-science requirements and solutions are discussed. A scenario involving adaptiveworkflows in Grids for Biomedical usage is discussed in order to enlighten a possible practical application of some work presented in this thesis.