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Service-oriented architectures have evolved to support the composition and utilisation of heterogeneous resources, such as services and data repositories, whose deployments can span both physical and organisational boundaries. The Semantic Web Service paradigm facilitates the construction of workflows over such resources using annotations that express the meaning of the service through a shared conceptualisation. While this aids non expert users in the composition of meaningful workflows, sophisticated middleware is required to cater for the fact that service providers and consumers often assume different data formats for conceptually equivalent information. When syntactic mismatches occur, some form of workflow harmonisation is required to ensure that data incompatibilities are resolved, a step we refer to as syntactic mediation. Current solutions are entirely manual; users must consider the low-level interoperability issues and insert Type Adaptor components into the workflow by hand, contradicting the Semantic Web Service ideology. By exploiting the fact that services are connected together based on shared conceptual interfaces, it is possible to associate a canonical data model with these shared concepts, providing the basis for workflow harmonisation through this intermediary data model. To investigate this hypothesis, we have developed a formalism to express the mapping of elements between data models in a modular and composable fashion. To utilise such a formalism, we propose additional architecture that facilitates the discovery of declarative mediation rules and subsequent on-the-fly construction of Type Adaptors that can translate data between different syntactic representations. This formalism and proposed architecture have been implemented and evaluated against bioinformatics data sources to demonstrate a scalable and efficient solution that offers composability with virtually no overhead. This novel mediation approach scales well as the number of compatible data formats increases, promotes the sharing and reuse of mediation rules, and facilitates the automatic inclusion of Type Adaptor components into workflows. |
