Technically, there is a myriad of specifications to choose from:
- The Business Process Modeling Notation (BPMN)
- The Java API for XML Web Services (JAX-WS)
- The WS-* specifications including the WS-I Basic Profile, WS-Addressing, WS-Policy, WS-Reliable Messaging, and WS-Security
- The Java API for RESTful Web Services (JAX-RS)
- The Java Business Integration (JBI)
- The Web Services Business Process Execution Language (WS-BPEL)
- The Service Component Architecture (SCA).
Each of these specifications has its raison d’etre and should be part of the architect’s toolkit. However, I find SCA quite intriguing. SCA defines a language neutral programming model for the assembly and deployment of services. SCA implementation types include Java, C++, Cobol, WS-BPEL, PHP, Spring, XSLT, XQuery, and OSGi bundles. SCA supports different bindings such as SOAP/HTTP Web services, JMS, RSS, and Atom. SCA applications can be hosted in web containers, application servers, and OSGi runtimes. SCA is geared toward the developer and can apply policies such as reliability, security, and transactions to services in a declarative manner. SCA has the support of big players including Oracle, SAP, and IBM. At the time of this writing, Sun Microsystems support for SCA is less than clear (to me anyway).
JBI is implemented by a number of Enterprise Service Bus (ESB) products. JBI defines a runtime architecture that allows plugins such as binding components and service engines to interoperate via a Normalized Message Router (NMR). Binding components (BCs) use communication protocols such as JMS, FTP, XMPP, and HTTP/S to connect external services to the JBI environment. Service engines provide application logic in the JBI environment. Examples of SEs are XSLT/XQuery data transformation engines, rules engines, and WS-BPEL engines. BCs and SEs do not communicate directly. They only communicate through the NMR. IBM, BEA (now part of Oracle) and SAP did not vote in favor of JBI Java Specification Request (JSR 208).
When starting a new SOA project, SOA architects will have to look beyond vendors politics and make some judgment calls about the best approach based on their business goals and functional requirements.
My personal take on this is to adopt an agile approach where new functionalities are implemented in an iterative manner. For example, instead of starting with an ESB infrastructure, a project can start by service enabling existing applications (code-first approach) with JAX-WS annotation capabilities or by creating new services with a contract-first approach where JAX-WS annotated service and server stub are generated from a WSDL. Alternatively, the Java API for RESTfulWeb Services (WS-RS) could be used when a RESTful approach seems more appropriate.
An ESB could later come into the picture in a context where you are connecting to multiple services (often across organizational boundaries) and there is a need for mediation services such as business process orchestration, business rules processing, data model transformation, message routing, and protocol bridging. In that context, JBI provides plug-and-play functionality in ESBs for service engines such as business rules engines and BPEL engines. For that reason, JBI can help avoid ESB vendor lockin (perhaps a reason why proprietary ESB vendors are not backing JBI).
However, SOA architects should carefully consider the benefits of the programming language and binding agnostic service assembly model proposed by SCA. This will be essentially a choice between centralized mediation and decentralized assembly. The Open Service Oriented Architecture (OSOA) group believes that JBI and SCA can actually work together for example to allow SCA components to call JBI components or to use JBI runtime containers to deploy SCA composites.
Decentralized assembly is agile and looks a lot more like the way the web itself works. So I believe that while the JBI model is fine for integrating legacy enterprise applications, new and future service-oriented applications will embrace the SCA approach.
So is the state of the union strong? There is certainly a risk of fragmentation. But choice will always drive innovation forward and that’s what attracts me to the Java platform in the first place.