OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help

sca-assembly message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]

Subject: ISSUE 56: Need to clarify definition of Bidirectional Interfaces -Additional Discussion


In last weeks' TC conf call, the discussion of Issue 56 was lively and important.

The discussion closed with the following motion on the table:

Proposed text for the Assembly specification (CD-01), to be added after line 2333

"In a bidirectional interface, the service interface can have more than one operation defined, and the callback interface can
also have more than one operation defined.  A single invocation of an operation on the service interface can cause
zero, one or many invocations of any of the operations on the callback interface and a single invocation of an operation on
the callback interface can result from one or from many invocations of any of the operations on the service interface.
For a given invocation of a service operation, which operations are invoked on the callback interface, the number of operations
 invoked, how they are correlated, and their sequence are not described by SCA.  It is possible that this metadata about
the bidirectional interface can be supplied through mechanisms outside SCA. For example, it might be provided as a written
description attached to the callback interface. "

I'd like to concentrate on the one aspect of this proposal that I think is not good - the outlawing of means for the correlation
of callback operations with forward operations.

First, I'd like to (again) discuss the impact that this has on applications.  If the system (SCA) provides no means for the
correlation of the callback operations, then it is left to the application writer(s) - in particular to the designer of the forward and
callback interfaces.  

Without any system provided correlation, the interface designer has to anticipate the correlation needs of the client (in
particular) - and must place elements into the business data that provide this correlation capability.  This will often go
beyond a simple parameter such as (say) "Order ID", since if the forward service interface provides multiple operations
relating to an order, the callback messages may well have to carry something like a "Request ID" in order to make it
clear to the client that a given response relates to a particular request that the client made - without this the client may
have real problems working out the true meaning of the callback operation.

I note that a single, consistent, system provided means of correlation of this type is preferable to the alternative of every
designer having to work it out for themselves.

Second, I note that numerous transport mechanisms including Web services and JMS (and related messaging subsystems)
provide a capability of marking a response message with an ID which indicates the request message that it relates to.
It is notable that the designers of these transport mechanisms considered it important to have this function, which has
the capability of permitting the client to establish which to original message a response relates, without the need to sort
through the business data.

I believe that it is reasonable for SCA to provide SCA applications with mechanisms to access this capability of underlying
transports, without the need for the applications having to resort to transport-specific APIs.

So, in summary, I continue to support the notion of SCA-provided correlation mechanisms - and that the Assembly specification
should assert that such mechanisms SHOULD be provided both by Bindings and by Client API specifications.

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

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

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]