Today, a technology newsletter carried an article about SCA (Service Component Architecture) which outshone at IBM campus along with BEA. Is it another SOA specification? Is it a SOA framework? Or, an alternate to SOA? Michael Rowley who is the author/architect/inventor of this said that it depends. Confused. Yes, it has been mentioned that SOA is hyped much and many of the things are futile.
Concept Behind SCA
Following are the key aspects of SCA:
- Services – A set of operations that perform logically related tasks
- Components – Contains the implementation and configuration of services
- Composites – Responsible for configuring services
- Domain – A physical environment where the components will be hosted for consumption
A service contains a service contract and address. Service contract specifies the operations available in the service, the inputs for which to operate and the promised outputs. Service address provides where the service contract is available for consumption. Components is nothing but C++ libraries or Java JARs. Composites are XML file which contains the map between service contract and its implementation. The domain enables to manage the components and apply policies for their access. It provides common communication infrastructure and extensibility stuff.
Technology behind SCA
Although in the specification, it has been mentioned that SCA is technology and language independent, it is majorly on Java. It has been mentioned that SCA is a concept as well as a framework but does not contain anything for presentation layer and data persistence. However, it integrates with Java based UI and DB frameworks.
So… What?
Instead of web services, SCA lets you connect and composite through web services, RPC or any other means, unlike today's protocol based SOA approach. This is what is mentioned and marketed in the SCA specification. When you are crossing the border of “Concept behind SCA” section of this post, you will be surprised that what is new in SCA for SOA, since WCF incorporated these few years ago when this specification was only on the paper. A more interesting and confusing thing is that the specification team invited Microsoft for adopting this into .NET. One more buzz is that this specification is based on WSDL. These two make me think what else has been proposed apart from what WCF has now with such a level of maturity.
For those who want a clear map between the above concepts and WCF:
- Services - C# interface with WCF declarations
- Components – C# classes with WCF declarations
- Composites – Service model section in app.config/web.config file
- Domain – Service host (IIS/WAS/Windows Process)
What Does It Have….What Doesn’t It Have?
It provides the following:
- Service reference – dependency with other services
- Composition – way to encapsulate technical/vertical components such as validation, logging and auditing components within service and hide these to the outworld.
- Policy - a statement that controls the operations that are provided by the infrastructure.
- Wire – a way for service aggregation and topologies (oneway, duplex, request and response)
- Bindings – provides the means to communicate to the consumers.
It doesn’t have the following:
- Service orchestration – but supports JSR based on BPEL
- Service extension
- Service inventory
Unfortunately, WCF has all the above with the power of .NET platform. So, beware of SCA jargon in the .NET world, where an elephant WCF has all the capabilities. As of my understanding, SCA is the WCF avatar in the Java world.
Michael Rowley saluted the WCF proposals and its features, however he tried to oversight it with SCA. It's confusing.
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