Mixing Workflows and Components to Support Evolving Services

Mixing Workflows and Components to Support Evolving Services

Françoise Baude, Virginie Legrand, Ludovic Henrio, Paul Naoumenko, Heiko Pfeffer, Louay Bassbouss, David Linner
DOI: 10.4018/978-1-4666-0255-7.ch019
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Composite distributed services involve local and remote services that get orchestrated according to specific business logic. This logic can be programmed by applying a traditional general-purpose programming language, but is generally described using a workflow language that coordinates a set of given services. The services involved in the composition, or the composition may need to evolve both at the business logic level (workflow level) and the global architecture level. This paper presents a solution to ease such evolution for compound distributed services and the authors’ proposal enables the evolution of both the business logic and the underlying architecture. This paper suggests relying on a distributed software component model to represent and easily manage the set of local or remote software entities (services) involved in the composition. Composite services are represented in a model that combines the use of a distributed and hierarchical software component model and new timed-automata based workflow language. This combination makes explicit the separation between functional and non-functional concerns, and as a consequence this approach helps in defining the required and various evolution procedures in context to compound services.
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General Context

Composing services and allowing services and their composition to evolve at runtime is crucial for most of distributed applications. Indeed, as soon as the execution environment may change in an unplanned manner, services must be able to adapt to those changes. In a more challenging manner, one could also expect services to evolve automatically in order to provide better quality of services, matching new user requirements, or providing users with unforeseen functionalities.

The context of the research work presented in this paper is the BIONETS European project, aiming at bio-inspired evolution of services and network protocols. In this context, we came out with a new composition model, integrating both workflow-oriented orchestration and component-oriented composition. Additionally, our composition model features high evolution and adaptation capacities. In this paper, we present this new model, the architecture it features, and the evolution capabilities it enables.

The originality and value-added of our model comes from the mixing -- and thus implied respective advantages -- of two service composition models, each specially focusing on some aspects of service composition: the workflow based composition approach mainly manipulates timed sequences of service invocations, whereas the component based approach focuses on the dependencies between ports of the different services forming a compound service.

A consequence and a particularity of this mixed composition model is that, as each of the model focuses on evolution, the compound model benefits from their respective evolution capabilities. Consequently, our model is particularly targeted at evolution of services and of their composition.

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