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RE: Application Protocol Definition (was RE: Visibility (was Re: Introducing the Service Oriented Architec tural style ...

From: Assaf Arkin <arkin@intalio.com>
Date: Thu, 27 Feb 2003 12:06:21 -0800
To: "Burdett, David" <david.burdett@commerceone.com>, "Mark Baker" <distobj@acm.org>
Cc: <www-ws-arch@w3.org>
Message-ID: <IGEJLEPAJBPHKACOOKHNOEFEDEAA.arkin@intalio.com>
Application Protocol Definition (was RE: Visibility (was Re: Introducing the
Service Oriented Architec tural style ...
  -----Original Message-----
  From: Burdett, David [mailto:david.burdett@commerceone.com]
  Sent: Thursday, February 27, 2003 3:34 AM
  To: 'Assaf Arkin'; Mark Baker; Burdett, David
  Cc: www-ws-arch@w3.org
  Subject: Application Protocol Definition (was RE: Visibility (was Re:
Introducing the Service Oriented Architec tural style ...


  Arkin

  You said ...

  >>> This of course doesn't help much, because we've just introduced three
different protocols, one described by HTTP, one described by WSDL and one
described by WSCI (just as an example). Again as with synch/asynch, this is
all a matter of applying a definition in the proper context.<<<

  It might not help, but it is real life. You do have multiple protocols
operating in combination at different "layers", for example (not sure this
list is complete or the names are right)

  1. Network infrastructure protocols, e.g. TCP/IP
  2. Communication protocols, e.g. HTTP
  3. Messaging protocols, e.g. ebXML Messaging or WS-RM
  4. Business protocols, e.g. Order placement protocol that defines sequence
of exchange of business documents

  You can also have other more slightly more specialized but still general
"protocols", e.g.
  5. Two phase commit, e.g. Business Transaction Protocol
  6. Discover protocol, e.g To discover a WSDL or Schema definition (REST
can work well here)
  7. Negotiation protocol, e.g. To negotiate which combination of protocols
1 through 4 to use in a specific instance

  ... we could probably go on ...

  The point is just calling some or all of these an "Application Protocol"
is, IMHO, insufficiently precise.

  Do you think we should try and define these types of protocol and what
they mean in more detail?

  I agree on both counts.

  For me the term 'communication' is as broad as the term 'application', so
for no. 2 I would actually prefer to use 'transport'.

  As James suggested, 5-7 are best categorized under 'utility'.

  arkin



  David

  -----Original Message-----
  From: Assaf Arkin [mailto:arkin@intalio.com]
  Sent: Wednesday, February 26, 2003 12:13 PM
  To: Mark Baker; Burdett, David
  Cc: www-ws-arch@w3.org
  Subject: RE: Visibility (was Re: Introducing the Service Oriented
  Architec tural style, and it's constraints and properties.



  > On Wed, Feb 26, 2003 at 03:18:48AM -0800, Burdett, David wrote:
  > > <DB>We need to define what we mean by an "application" if you mean it
is
  > > anything above the transport layer, then you are correct but
  > really I think
  > > the layers are typically: Operating System, App Server, "Web Services
  > > Middleware", Application.

  How about:

  Application - A program designed to assist in the performance of a
specific
  task, such as word processing, accounting, or inventory management

  Now the only question is 'what application are we talking about?'

  Are we talking about the HTTP or FTP server? In this case HTTP and FTP are
  the application protocols.

  Are we talking about accounting? In this case the accounting protocol is
the
  application protocol.

  Is it possible to have an application on top of an application on top of
an
  application? How about my accounting application running inside a WS
  container (in itself an application) implemented inside an HTTP server (in
  itself an application). Is that possible?

  This of course doesn't help much, because we've just introduced three
  different protocols, one described by HTTP, one described by WSDL and one
  described by WSCI (just as an example). Again as with synch/asynch, this
is
  all a matter of applying a definition in the proper context.

  arkin

  >
  > The *critical* thing that one has to accept in order to understand REST,
  > is that application protocol methods are the same as operations in an
  > API, i.e. at the same layer of the stack as "getStockQuote" or
  > "purchaseBook".  If you just take this as a given for a moment, you'll
  > see that all the arguments I've ever made on this subject become a big,
  > complex, yet entirely self-consistent description of much of Web
  > architecture, and indeed several other Internet scale architectures.  If
  > you don't accept it, then I probably come off as a loon, which I
  > completely understand because I thought the same thing of some guys who
  > saying that to me back in 97/98 (Dan Connolly and Roy Fielding, FWIW).
  >
  > So, a *rhetorical* question for those of you who don't believe that
  > GET is at the same layer as getStockQuote; what would you call a
  > protocol that does have a "getStockQuote" method?  Note; "application
  > protocol" is already taken. 8-)
  >
  > MB
  > --
  > Mark Baker.   Ottawa, Ontario, CANADA.        http://www.markbaker.ca
  > Web architecture consulting, technical reports, evaluation & analysis
Received on Thursday, 27 February 2003 15:08:01 GMT

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