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RE: Issues, trout ponds and other dangerous regions

From: Cutler, Roger (RogerCutler) <RogerCutler@chevrontexaco.com>
Date: Tue, 18 Feb 2003 11:51:43 -0600
Message-ID: <7FCB5A9F010AAE419A79A54B44F3718E01624A5A@bocnte2k3.boc.chevrontexaco.net>
To: www-ws-arch@w3.org

I don't entirely understand this discussion, but it sounds to me like
David and Frank have rather different conceptions of what the words
"service" and "resource" mean.  If so, it seems to me that it would be a
good idea to get on the same page somehow.

-----Original Message-----
From: David Orchard [mailto:dorchard@bea.com] 
Sent: Monday, February 17, 2003 6:12 PM
To: www-ws-arch@w3.org
Subject: RE: Issues, trout ponds and other dangerous regions



0.  In general, I'm not really sure what changes you are suggesting to
the text or approach that I took.  I get the point #1 about GET/POST,
perhaps there's too much.  But on the other ones, it's almost like you
are saying that describing the architectural style of SOA is a bad thing
to do.  I think you are implying that services and resources are
separate things, therefore can't and shouldn't be compared/constrasted.
Also that the generic vs specific interface is a can 'o worms, so we
shouldn't talk about it.  I must admit I'm astounded by our groups
ability to talk about things that we want to talk about.  eek.  Now I'm
talking about us talking about us talking about something.  I was just
hoping to write up something that could appear in our actual text,
rather than debating whether we should do the text or not.  I'll try to
explain in the rest of this note, my motivations.

1. I make the assumption that there is something architecturally to
define about Web services.  Given that it is technologically neutral, it
is probably an architectural style that Web services are.  I "bang on
about" POST/GET for illustrative purposes mostly.  Indeed, I
specifically chose the nefarious getStockQuote to allow the description
of the style to "fess up" about it's constraints, and how they are
different and similar to REST. <hint>I think that TAG will give pretty
strong pushback on a ws-arch that doesn't describe it's architecture in
relation to web architecture.  Saying "xml, uris, maybe soap, maybe wsdl
won't cut it".  BTW, I would vote this way on the TAG if asked - and I'm
SURE somebody will ask the TAG.  I just happen to take enough personal
responsibility that I think I should volunteer to help provide such a
description to avoid such pushback.  Of course, the ws-arch could ignore
such TAG feedback.  Maybe the Director will even let it pass.  But why
cause more trouble for ourselves than we need to</hint>

2. I would like to end up with a description of the architectural style,
and the trade-offs associated with that style.  These trade-offs must be
based upon requirements or properties.  Given that the usual criticism
of Web services has been by "REST" folks, I thought that coming up with
a description and trade-offs in the same vernacular that is used for the
only real definition of REST would be helpful in getting to consensus on
similiarities/differences.  Hence the choice to use the properties from
Roy's thesis as the basis for description of properties for SOA, and
hence the choice of trade-offs in the same style that Roy uses in his
sections 4 and 5.  Further, I'm lazy.  So therefore, I chose to re-use
Roy's properties and architectural style descriptions, rather than
recreate the description of REST in some third party methodology.

3. I would like to end up with a harmonized Web architecture and Web
Services architecture, from glossary terms to styles discussions to
properties.  I really do believe that this is possible.  BTW, when I say
"harmonized", I specifically mean that there are references from web
services arch to web arch, and it includes
changes/extensions/refinements to web arch "things".  I HIGHLY doubt
that the TAG is going to choose a vendor-specific architecture
methodology.  So we need to find some way of getting to a common
methodology.  Again, I simply don't have the time or energy to come up
with yet another darned methodology.

4. I think that the definition of "Resource" as an entity that has
actual presence is not a widely accepted definition.  I find it somewhat
interesting that the URI spec does not define what Resources are, and
leaves it to something like RDF, which says

"Resources All things being described by RDF expressions are called
resources. A resource may be an entire Web page; such as the HTML
document "http://www.w3.org/Overview.html" for example. A resource may
be a part of a Web page; e.g. a specific HTML or XML element within the
document source. A resource may also be a whole collection of pages;
e.g. an entire Web site. A resource may also be an object that is not
directly accessible via the Web; e.g. a printed book. Resources are
always named by URIs plus optional anchor ids (see [URI]). Anything can
have a URI; the extensibility of URIs allows the introduction of
identifiers for any entity imaginable. "

So there doesn't appear to be anything that's not a resource.  It's
anything imaginable.  It's fairly easy for me to see that a Web service
is ALWAYS a resource.  It's a particular type of a resource, as noted in
our definition which says that a Web service is identified by a URI - a
Web service is identified by a URI, URIs are for Resources, therefore a
Web services is a resource.

5. Are you saying that a Service MUST have a description, otherwise it's
not a service?  Do you mean a WSDL realization of that description?  And
how is that *REALLY* different than the web?  Each web page that I look
describes to me how to use it - otherwise I wouldn't know which links to
select! :-) I have been trying to avoid the requirement that a service
has a formal description.  And saying a web service is describable in
WSDL is I think terrible as well - as WSDL can describe anything that
the group chooses to describe!

6. I don't get the distinction between service provider and resource
provider.  See my item #4 on the relationship between resources and
services.

7. As for generic vs specific, I don't think it's a can of worms to
describe it, or the benefits.  Where I expect, and have already gotten,
the pushback is when some of the benefits acrue.  As in, "some kinds of
applications are better styled in a SOA" manner, with the pushback of
"oh yeah, I've never seen one".  BTW, I'm hoping that the comparison of
a few different use cases of app development will flesh out the point
that you are making, that is the the objects and verbs must both be
understood.  This shows up in the visibility property elaboration.
Course, while I spend time justifying what I'm doing, I can't actually
be doing the doing of the scenarios, SOA references etc.

Cheers,
Dave

> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of Francis McCabe
> Sent: Monday, February 17, 2003 2:04 PM
> To: www-ws-arch@w3.org
> Subject: Issues, trout ponds and other dangerous regions
>
>
>
> David gives an eloquent defense of REST in 
> [http://www.w3.org/2002/02/mid/ 
> 007d01c2d325$5c30fc00$c10ba8c0@beasys.com;list=www-ws-arch];
> however it
> appears that he re-opens issues that need resolving.
>
> In the current WSA document, in several places, it is stated that Web
> services are NOT tied to specific technologies and protocols
> (such as
> HTTP, SOAP, WSDL etc.) In fact, currently, the ONLY hard nailed-down
> technology choices are URIs and XML.
>
> If the WSA is to be technology neutral, then it is not appropriate to
> `bang on about' POST vs GET in the document; although
> constraints such
> as idempotency are definitely `in scope'. On the other hand,
> if the WSA
> is to be technology centered, then we need to make that choice
> explicit, and soon.
>
> The second nettle is more conceptual: the distinction between 
> resources and services. There is a relationship, but perhaps not one 
> that is immediately obvious. In my opinion these concepts are at 
> different levels of abstraction: a resource is an entity that has an 
> actual presence and a service is a means of achieving tasks.
> Services require
> realizations, and such realizations are resources; but
> resources can be
> `of' anything and are not tied to services. On the other
> hand, services
> have descriptions which are not of the service itself but of how to
> interact with them.
>
> This distinction is important because, if the focus is on services as
> opposed to resources, then a large number of concepts need to
> be `put
> into place' that have no relevance to the strict resource
> view. A good
> example is the service provider. It is an important concept for a
> service oriented architecture; but has no special equivalent for
> resource. (Owner, however, is a concept that applies to both.)
>
> Finally, there is the hoary old one concerning generic interfaces vs.
> specific interfaces. Again, so far, we have been pretty
> muddled about
> this. [Personal opinion: it is not possible to completely
> capture the
> semantics of a message without grasping both the verb and the
> object of
> the message. Definitely there are different styles of architecture,
> where there is a rich though generic set of verbs that everyone is
> expected to agree on, and where there is an essentially
> infinite set of
> verbs and everyone is expected to come up with their own
> definitions. I
> am somewhat persuaded of the merits of the generic case; but
> its a can
> o'worms defining the spanning set.]
>
>
Received on Tuesday, 18 February 2003 12:52:24 GMT

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