RE: [sca-assembly] RE: [ASSEMBLY-31] Wiring from a reference with nobinding to a service with a binding

[Simon Nash <NASH@uk.ibm.com>]

I don't want to spoil the party, but...

It's clearly fine to do this local optimization for <binding.sca>.  But it 
is OK to do this for <binding.jms>?  To make this safe, it would be 
necessary to ensure that all observable JMS semantics are preserved.  Are 
we agreed that any local optimization would need to do this?

    Simon

Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156  Fax +44-1962-818999



"Peshev, Peter" <peter.peshev@sap.com> 
06/12/2007 14:03

To
Mike Edwards/UK/IBM@IBMGB, "OASIS Assembly" 
<sca-assembly@lists.oasis-open.org>
cc

Subject
RE: [sca-assembly] RE: [ASSEMBLY-31] Wiring from a reference with no 
binding to a service with a binding






Hi Mike,
 
At least to me that's very good model and clear description that solves 
nicely  ASSEMBLY-1 & 31 as long the last paragraph is kept.
 
Best Regards
Peter
From: Mike Edwards [mailto:mike_edwards@uk.ibm.com]   
Sent: Thursday, 6. December 2007 11:36
To: OASIS Assembly
Subject: RE: [sca-assembly] RE: [ASSEMBLY-31] Wiring from a reference with 
no binding to a service with a binding


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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741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU 












Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU