INT: Re: Intermediary Discussion

OK, there has been *some* discussion of this topic [1-2]. The Abstract Model
Group have also been thinking about intermediaries[4-5]. Mark Nottingham has
posted a document discussing intermediaries[3].

After reading these posts I think we are still some way from consensus on
*exactly* what an XP intermediary is but we do seem to have broad agreement
that;

1.    XP Intermediaries sit between the sender of a request and the ultimate
recipient of that request.

2.    XP Intermediaries perform some processing of the request message.

3.    Exactly what processing occurs at an intermediary is defined by
extension blocks.

4.    There needs to be a way of addressing intermediaries from within an XP
message.

5.    There may be multiple intermediaries between the sender and the
receiver.


Open questions/issues...

Do XP Intermediaries also sit between the sender of the response and the
ultimate receiver of that response? And hence also process the response
message assuming one exists.

If the answer to the above question is 'Yes' is the set of intermediaries
the same for both the request and response message?

If a given intermediary is the 'target' for more than one extension block in
an XP message does a processing order need to be defined and is so how do we
define it?

In terms of addressing intermediaries it's my feeling that we need to
address ( ahem ) the following cases;

      a) absolute addressing ( must go to machine A )
      b) by group ( must go to one of machine X, Y or Z )
      c) by class ( must go to a machine running Windinux )


So, coming to the purpose of this discussion which was to provide a new
definition for XP intermediary here are few possibilities;

1.    Taken from Hugo's mail ( thanks Hugo! )

  An XML Protocol intermediary is an application which processes a
  defined set of blocks in an XML Protocol message along an XML
  Protocol message path. It acts both as an XML Protocol receiver and
  an XML Protocol sender in order to forward the XML Protocol message
  towards the ultimate XML Protocol destination.

2.    Slight amendment to the above to add notion of addressability

  An XML Protocol intermediary is an application, addressable from
  within an XML Protocol message, which processes a defined set of
  blocks in an XML Protocol message along an XML Protocol message path.
  It acts both as an XML Protocol receiver and an XML Protocol sender
  in order to forward the XML Protocol message towards the ultimate
  XML Protocol destination.


3.   Slight amendent to 3 to make the possibility of multiple intermediaries
more explicit

  An XML Protocol intermediary is an application, addressable from
  within an XML Protocol message, which processes a defined set of
  blocks in an XML Protocol message along an XML Protocol message path.
  It acts both as an XML Protocol receiver and an XML Protocol sender
  in order to forward the XML Protocol message to the next recipient
  in the message path which may be another XML Protocol intermediary
  or the ultimate XML Protocol destination.


Thoughts, comments, flames etc. all welcome...

Gudge

[1] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0006.html
[2] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0011.html
[3] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0026.html
[4] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0021.html
[5] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0023.html

Received on Tuesday, 6 February 2001 17:20:46 UTC