I am not saying you *must* have an 'intermediary', just that it is a useful pattern in many scenarios.
Lawrence --- In [email protected], "Rob Eamon" <rea...@...> wrote: > > --- In [email protected], "l.wilkes@" > <l.wilkes@> wrote: > > > > Perhaps I used the wrong term, sorry... > > > > But if the intention is to isolate the service from changes to the > > implementation, then some form of 'intermediary' is useful. Call it > > facade, wrapper, what you will. > > The service interface is the piece that isolates the service implementation > from the rest of the world. > > > Often the 'intermediary' can be something like an ESB, where most > > ESB products can host the service endpoint, and act as the > > intermediary to the implementation, providing the transformation > > and mapping technologies to marry the two together. > > I think it is important not to view the ESB as an independent actor. > ESB-hosted components should be viewed as a part of the consumer or the > provider. Consumers do not have a contract with the ESB, they have a contract > with the service, which is accessed via the ESB. The ESB might be but one of > multiple interfaces a service exposes. > > The ESB most times will host a service interface (a single ESB will host > interfaces for multiple services). It might also host consumer helper > components. > > For example, the service interface exposes a particular message format on a > particular communications path (e.g. the ESB). To use the interface a > consumer *must* use the particular message format on that particular path. > The consumer might need help to create the necessary format and can use the > ESB to do so. Thus, that ESB component that does the mapping is part of the > consumer. > > > More often than not, this is exactly what we find many of our > > clients faced with when providing service interfaces on top of > > existing implementations. > > > > But equally, given that change is a constant, it seems a good > > pattern to adopt when implementing any service. > > I'm with Michael. Calling the service interface a "facade" seems odd. It > implies something additional is present but in reality it is already there. > All service interfaces are facades--the face of the service. > > -Rob >
