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Subject: RE: [sca-assembly] RE: [ASSEMBLY-31] Wiring from a reference with nobinding to a service with a binding
- From: Mike Edwards <mike_edwards@uk.ibm.com>
- To: "OASIS Assembly" <sca-assembly@lists.oasis-open.org>
- Date: Thu, 6 Dec 2007 09:35:50 +0000
Peter,
After some private discussions of the
issues with Dave, I now believe that Dave's proposal is
the right one. The treatment of
services should not be exactly the same as the treatment of
references.
Creating a proxy object for a reference
is a very different process from the business of
creating an endpoint for a service.
It is reasonable for an SCA runtime
to know in advance what endpoints it has to create for
the services present in the domain -
and that the idea that new endpoints have to be created
merely to satisfy a new client reference
turning up somewhere in the domain is not reasonable.
So, I think that the principle for a
service needs to be that there will be an endpoint created
for each binding explicitly declared
for the service, with the existence of a binding.sca
endpoint IF no explicit binding is specified.
The point you make in the last paragraph
below, I believe DOES apply to references. So, for
a reference, a "binding.sca"
(either implicit or explicit) can be taken to mean "give me a connection
to the target service(s), using whatever
communication means are available". In this case,
I think that the proxies given to the
component for the reference could each deal with a separate
protocol and that the protocol used
simply "matches" the target service's protocol.
I agree - in these cases the protocol
used by the proxy is irrelevant to the implementation code.
IF the reference or the service requires
a particular protocol for some reason, then that need
should be expressed via an intent and
the presence of the intent would then limit the range of
protocols that can be used.
So, I think it gives us a clean model
where:
a) For services, you get endpoints for
each explicitly declared binding, with the default of
binding.sca if there is no explicit
binding. Multiple bindings imply multiple endpoints.
b) For references, you get proxies using
any of the declared bindings, with the default of
binding.sca if there is no explicit
binding. The binding actually used for a given wire depends
on the binding(s) attached to the target
service, where the principle is to select compatible
bindings (for the moment, I take that
to mean the binding types must be the same).
In addition, binding.sca is "flexible"
for the purposes of wiring and will match ANY binding
on the target service(s).
I think that this is the simplest model
and avoids the problem associated with the model which
you have proposed, that binding.sca
may or may not be present depending on whether it
can or cannot satisfy the intents attached
to the reference.
I think that the model I propose has
the merit of simplicity and encourages the creation of
simple compositions, where most references
to targets within the domain either have no
explicit binding at all (the 80% case)
or have binding.sca attached, while any service endpoints
which need an explicit binding attached
in order to be available outside the domain don't
have to be concerned about additional
endpoints being necessary for clients within the
domain.
I note that the principle of "optimised
communication" between clients and providers that
run on the same machine or within the
same process, is not affected by this model. The
runtime is ALWAYS free to optimise communications,
as long as the interfaces to both
client and provider code are honoured.
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
Email: mike_edwards@uk.ibm.com
"Peshev, Peter" <peter.peshev@sap.com>
wrote on 06/12/2007 08:51:22:
> Hi Mike,
>
> OK, I understand we have different opinion between me and you + Dave
>
> But can you help me understand why ? I guess you are afraid that the
> component may break without binding.xyz in the scenario below. However
> the contract between the SCA assembly and the programming technology
is
> the interface that is on the service. If the SCA runtime can construct
> objects fulfilling the interface, then what is the problem ?
>
> I.e. does it makes a difference for a component with interface.wsdl
> whether its XML-ish data objects in the interface were received
via
> HTTP POST operation, via SOAP over JMS, or by direct local call ?
>
> Best Regards
> Peter
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