Flexible Service Composition

Service-oriented architectures are a popular architectural paradigm for building software applications from a number of loosely coupled, distributed services. Through a set of procedural rules, workflow technologies define how groups of services coordinate with one another to achieve a shared task. A problem with workflow specifications is that often the patterns of interaction between the distributed services are too complicated to predict and analyse at design-time. In certain cases, the exact patterns of message exchange and the concrete services to call cannot be predicted in advance, due to factors such as fluctuating network load or the availability of services. It is a more realistic assumption to endow software components with the ability to make decisions about the nature and scope of their interactions at runtime. Multiagent systems offer a complementary paradigm: building software applications from a number of self interested, autonomous agents. This thesis presents an investigation into fusing the agency and service-oriented architecture paradigms to facilitate flexible, workflow composition. This proposed agent-based approach to workflow composition is founded on the concept of shared interaction protocols that allow groups of agents to communicate in open systems. By adopting an agent-based approach to workflow composition, active autonomous agents can utilise the typically passive service-oriented architectures, found in Internet and Grid systems. In contrast with statically defined, centralised workflows, decentralised agents can perform service composition at runtime, allowing them to operate in scenarios where it is not possible to define the pattern of interaction in advance. Application to real scenarios is a driving factor behind this research. By working closely with a number of active Grid projects, namely AstroGrid and the Large-Synoptic Survey Telescope (LSST), a concrete set of requirements for scientific workflow have been derived based on realistic science problems. This research has resulted in the MultiAgent Service Composition (MASC) language to express scientific workflow, methodology for system building and a software framework which performs agentbased web service composition, in order to enact distributed e-Science experiments. Evaluation of this thesis is conducted through case study, applying the language, methodology and software framework to solve a motivating set of workflow scenarios.