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RE: XP Service URIs

From: Henrik Frystyk Nielsen <frystyk@microsoft.com>
Date: Wed, 22 Nov 2000 07:40:13 -0800
Message-ID: <008701c0549a$8d5ea220$6701a8c0@redmond.corp.microsoft.com>
To: Oisín Hurley <ohurley@iona.com>, <xml-dist-app@w3.org>
> >Allowing optional expression of destination URI sounds like
> a good idea.
> In fact, I think mandatory expression of the destination URI is even
> better. There has been some conversation about the need to identify
> the service instance endpoint in a separate manner to the protocol
> instance endpoint. That is, to identify the XP processor for whom
> the message is intended.

I like the idea of requiring that there be a *description* of how the
<ultimate XP receiver>  can be obtained from either the <xp binding> or
the <xp message>. I don't like the idea of requiring that the
request-uri must be in the <xp message> - it is just as valid that it be
indicated by the <xp binding>.

Note, that I have emphasized the terms defined by [1] by using <foo>
notation - I encourage people to use these terms (and to comment on the
terms document [1]).

There is an illustration of the <xp message path> model in [2]. An <xp
receiver> is identified by a URI and the <ultimate xp receiver> is an
<xp receiver> as any other receiver in this regard. That is, we only
need one URI for the <ultimate xp receiver>.

The next question is where to carry that URI. If using XP in combination
with HTTP, SMTP or similar, it makes sense to use the mechanisms already
defined by these protocols to indicate the destination. The reason is
that because HTTP, SMTP etc. indicate the destination of HTTP and SMTP
messages themselves, it doesn't matter what is written in the <xp

  xp sender ---> ultimate xp receiver

  xp sender ---> ultimate xp receiver

However, if there is no such mechanism (for example if running XP
directly on top of TCP) *or* one wants to use multi-hop links with
multiple <xp bindings> like this

  xp sender ---> xp intermediary ---> xp intermediary ---> ultimate xp
            http                 smtp                 http   receiver

then it makes sense to say that there must be a mechanism within the <xp
message> indicating who the <ultimate xp receiver> is.

Sp, as it depends on the <xp binding> and the <xp message path> where to find
the URI of the <ultimate xp receiver>, it makes sense to have a mechanism
defined as an <xp module> where it can be marked as either optional or
mandatory. That way, it can be used when needed and not used if not needed.


[1] http://www.w3.org/2000/xp/Group/xp-terms-01.html
[2] http://www.w3.org/2000/xp/Group/xp-terms-01.html#N3030
Received on Wednesday, 22 November 2000 10:41:06 UTC

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