Section: Software

Supporting Service Orchestrations over Heterogeneous Interaction Paradigms

Participant : Nikolaos Georgantas [correspondent] .

Established architectural paradigms enabling open system integration, such as service oriented architecture (SOA) and enterprise service bus (ESB), have provided answers to the essential issue of interoperability in distributed systems. However, realizations of these architectural paradigms fall short when it comes to integrating systems featuring heterogeneous interaction paradigms, such as client/server (CS), publish/subscribe (PS) and tuple space (TS), due to the differing interaction semantics of the latter. Typical solutions constitute in wrapping any system behind RPC-based service interfaces, which results in partial loss of interaction semantics. This can cause suboptimal or even problematic system integration.

Aiming at enabling seamless integration of heterogeneous interaction paradigms, we introduce an interoperability solution based on abstraction and merging of their common high-level semantics, paying special attention to the preservation of semantics. To this end, we propose three abstract connector types for the CS, PS and TS interaction paradigms. We further introduce a higher-level generic application (GA) connector type, which provides an abstract union of the three models, thus preserving their interaction semantics. We express our connector types in terms of application programming interface (API) primitives and related interaction protocol semantics. We then apply our abstractions to rethink a typical SOA- and ESB-based orchestration of heterogeneous distributed systems. Our solution features:

• Extending the BPEL workflow language with GA API primitives in terms of extension activities enabled by the BPEL specification;

• Introducing XSLT transformation between the GA-extended BPEL and the standard BPEL, which consists of encapsulating GA primitives into standard BPEL primitives and enables conveying GA semantics on top of BPEL primitives and subsequently on top of the common bus protocol primitives;

• Providing Java code templates for systematic and highly facilitated building of ESB-embedded binding components;

• Proposing interface description languages in the form of XSDs for systems employing CS-, PS-, TS-, and GA-connectors; and

• Introducing XSLT transformations between native system interface descriptions and GA-based interface descriptions.

We have developed our solution on top of the PEtALS ESB, which provides inherent support for BPEL by embedding the EasyBPEL workflow engine. Our solution considerably facilitates the application developer in designing and executing heterogeneous orchestrations. Furthermore, it is highly extensible, enabling easy integration of support for new middleware platforms. To demonstrate the applicability of our approach, we have implemented an application workflow integrating a JMEDS DPWS Web Service (CS), a JMS system based on Apache ActiveMQ (PS), and a Jini JavaSpaces system (TS). Our software will soon be released under open source license.