Specification and Verification of Context-dependent Services

Current approaches for the discovery, specification, and provision of services ignore the relationship between the service contract and the conditions in which the service can guarantee its contract. Moreover, they do not use formal methods for specifying services, contracts, and compositions. Without a formal basis it is not possible to justify through formal verification the correctness conditions for service compositions and the satisfaction of contractual obligations in service provisions. We remedy this situation in this paper. We present a formal definition of services with context-dependent contracts. We define a composition theory of services with context-dependent contracts taking into consideration functional, nonfunctional, legal and contextual information. Finally, we present a formal verification approach that transforms the formal specification of service composition into extended timed automata that can be verified using the model checking tool UPPAAL. In [12] and [11], we introduced a formal framework, called FrSeC, that supports the specification, publication, discovery, selection, composition and verification of services with context-dependent contracts. The work reported in this paper is founded on this framework. We provide a formal specification of services with context-dependent contracts and their compositions. The composition theory of services takes into consideration the functional, nonfunctional, legal, and contextual aspects of services. We also present a formal verification approach that transforms the formal specification of service composition into UPPAAL [2] timed automata in order to verify service properties using model checking. Service-oriented Architecture (SOA) is an emerging view of the future of distributed computing and enterprise application development [4]. However, current approaches for the specification, publication, discovery, selection, and provision of services fall short in important respects. First, the relationship between the service contract and the conditions in which the service can guarantee its contract has been ignored, however these are necessary in order to associate the context of the service provider and the context of the service requester. Second, contextual information [3] is not well represented and not rigorously applied in service discovery and service provision. Third, current composition approaches compose only service functionality and ignore nonfunctional requirements. Thus, service contracts, and context information that are part of services are left out of the composition, and verification. Fourth and the last, the published approaches do not use formal methods for the specification of services, contracts, contextual representation and application, and service composition. Without a formal basis it is not possible to justify through formal verification the correctness conditions for service compositions and the satisfaction of contractual obligations in service provisions. The work reported in this paper eliminates these shortcomings. The basic building unit for SOA-based applications is service. It is normally understood that service is an autonomous and platform-independent software program, having its own distinct functionality and a set of capabilities related to this functionality. These capabilities are usually invoked by external consumer programs and are usually expressed via a published service contract. A service contract