Re: multiple MEPs per binding

+1!

Christopher Ferris
STSM, Software Group Standards Strategy
email: chrisfer@us.ibm.com
blog: http://www.ibm.com/developerworks/blogs/dw_blog.jspa?blog=440
phone: +1 508 377 9295

Noah Mendelsohn/Cambridge/IBM wrote on 03/07/2006 10:43:23 AM:

> Mark Baker writes:
> 
> > On 3/7/06, Jean-Jacques Moreau <jean-jacques.moreau@crf.canon.fr> 
wrote:
> > >
> > > Noah Mendelsohn wrote:
> > > > * Always, or almost always, if a binding supports more than
> > one MEP, then the one in use will have to be discoverable from 
> > information in the non-envelope part of the transmission.
> > > .. or out-of-band!
> > 
> > Eek!  I hope not.  8-O That would mean that two byte-for-byte
> > identical messages might have different meaning dependent upon what
> > service receives it.  Amoungst other things, that would rule out many
> > asynchronous cases where, if the WSDL changes between the time the
> > message is sent and received, then communication becomes ambiguous.
> > 
> > If it's important to the meaning of the message, it should be in the
> > message IMO.
> 
> I strongly agree with Mark on this.   It's very important on the Web and 

> in other flexible networks that individual messages be reasonably 
> self-describing.  IMO, the role of WSDL is to give advance information 
and 
> a way of documenting contracts in advance >for those who wish to have 
that 
> advance knowledge<.  In general, it is undesirable to rely on such out 
of 
> band information in determining what the protocol is.   Some judgement 
is 
> required in all this, but as  general rules of thumb I have tried to 
> follow over the years:
> 
> * WSDL should not be required to use SOAP properly, or to successfully 
> implement a given use of SOAP.
> 
> * Even if one end of the connection benefits from having WSDL for 
planning 
> its code, the other end should not necessarily require it.  For example, 

> you can easily imagine a large scale enterprise that offers services to 
a 
> wide range of communicating partners.  The large enterprise uses WSDL to 

> define its interfaces, and to help generate its code.  It offers the 
WSDL 
> for those partners who wish to use it in preparing their code.  On the 
> other hand, if some PERL or PHP programmer wants to just get the SOAP 
> message, look at it, and respond to it, they should be able to just read 

> the SOAP and HTTP specs, and follow their noses from their.  I.e.  HTTP 
> well tell you things like the WebMethod and the media type 
> application/soap+xml, which will determine that SOAP is in use and which 

> SOAP MEP to use.  Once you know that, you know to use the SOAP 
processing 
> model on the message, and therefore that you need to understand the 
QNames 
> of the header, the contents of the body, etc.  No WSDL required.
> 
> Noah
> 
> --------------------------------------
> Noah Mendelsohn 
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
> 
> 
> 
>