[sca-assembly] Composition Question

[Mark Hapner <Mark.Hapner@Sun.COM>]

When an SCA component uses a service provided by some entity on the  
web say Google Search, Paypal payments, or any service it expects is  
available for access via the net, this dependency is fundamentally  
different from using a 'service' whose implementation it expects to be  
'composited' with in a deployable bundle.

SCA expects services in a composite to provide the full range of SCA  
metadata and to be 'typed' so that alternative implementations can be  
substituted. Services on the net are often provider specific. No one  
expects to be able to substitute a NetSuite CRM data service for a  
SalesForce CRM data service, i.e. there are no service 'types' on the  
net - just unique service instances.

Clearly, implementing services that rely on network services that you  
have no control over and that are unique is a very common case.

I don't seem to find anything in the SCA assembly spec that formally  
treats this case as a 'first class' part of the service composition  
problem. At best, it seems to be treated as a degenerate case that SCA  
doesn't need to deal with beyond what is already defined by Soap,  
WSDL, etc.

Is this the case, or does SCA provide metadata that simplifies  
composing these, by definition, non-compositable, services? Is it  
correct to say that SCA is focused on composing service  
implementations into composite deployment bundles and leaves  
composition across independent, network services to other  
technologies? Is it expected that network services will find it useful  
to provide SCA 'typing' metadata even though they will never be  
'instanced' with properties nor 'composed' within SCA composites?

-- Mark