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

["Peshev, Peter" <peter.peshev@sap.com>]

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

---

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