Interaction design in service compositions

This thesis proposes a concept and transformations for designing interactions in a service composition at related abstraction levels. The concept and transformations are aimed at helping designers to bridge the conceptual gap between the business and software domains. In this way, the complexity of an interaction design can be managed adequately. A service composition is specified as one or more interactions between application components. Interaction design is therefore the central activity in the design of a service composition. Interaction design at related abstraction level requires an interaction concept that can model interactions at a higher abstraction level (called abstract interactions) and interactions at a lower abstraction level (called concrete interactions), in order to avoid any conceptual gap between abstraction levels. An interaction is defined as a unit of activity that is performed by multiple entities or participants in cooperation to establish a common result. Different participants can have different views on the established result. The possible results of an interaction are specified using contribution constraints and distribution constraints. Contribution constraints model the responsibility of the participants in the establishment of the interaction result. Distribution constraints model the relation between the participants’ views. An interaction provides synchronisation or time dependency between the participants on each other. This interaction concept can model abstract and concrete interactions. A designer can hence use a single interaction design concept during a design process. Two design transformations are defined, namely interaction refinement and interaction abstraction. Interaction refinement replaces an abstract interaction with a concrete interaction structure. Interaction abstraction replaces a concrete interaction structure with an abstract interaction. A set of conformance requirements and a conformance assessment method are defined to check the conformance between an abstract interaction and concrete interaction structure. In an interaction design process, a designer first represents a service composition as an abstract interaction that specifies the desired result. This abstract interaction is then refined into a concrete interaction structure that specifies how to establish that result. Interaction refinement can be done recursively until it results in a concrete interaction structure that can be mapped onto available interaction mechanisms. Every refinement is followed by conformance assessment. To facilitate the development process of a service composition, this thesis provides – patterns for interaction refinement, which serve as guidelines on possible refinements of an abstract interaction; – abstract representations of interaction mechanisms, which allow interaction mechanisms to be included in an interaction design at a higher abstraction level; and – a transformation tool to transform an interaction design at an implementation level to an executable implementation. The use of the interaction concept, design transformations, patterns for interaction refinement, abstract representations of interaction mechanisms, and transformation tool are illustrated with two case studies. In the first case study, we design a travel reservation application as a service composition using a top-down design approach. The services and application components that are involved in the service composition have to be developed. In the second case study, we design enterprise application integration for an order management that composes existing services and applications. We follow an integration approach and use our interaction concept during the design process. The obtained integration solution is then transformed to an executable implementation using our transformation tool.