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RE: D-AG0008: "is coherent and consistent in its definition"

From: Austin, Daniel <Austin.D@ic.grainger.com>
Date: Fri, 22 Mar 2002 17:22:13 -0600
Message-ID: <E0995D588DC3D211BB8D00805FFE353907358BDD@ic.ic.grainger.com>
To: "'Timothy N. Jones'" <tim@crossweave.com>, www-ws-arch@w3.org
Hi Tim,

	Just a few comments on your write-up on goal 8. I don't believe that
we should use the words "complete" or "self-contained". I don't think that
either of these applies to an achitecture in general, and especially not to
one that intends to apply to an unknown problem domain such as Web Services.
We are not in a position to be able to determine completeness, and in fact I
believe that we cannot and should not attempt to design the architecture
with this idea in mind, but that we should explicitly design it to be an
open architecture that provides sufficient flexibility to allow for the
addition of new technologies and services as yet unknown.

	One issue regarding this goal: this goal talks about the definition
of the architecture, i.e. the reference architecture that we define. This
reference architecture should be consistent and coherent. This applies to
both the reference architecture itself and the document that contains its

	To be honest, I don't understand your defintiions of consistency and
coherence. Further, I don't see what OOP design patterns or simplicity have
to do with either, as these issues seem to me to be orthogonal. Here is a
loosely worded definition of what I mean when I say "consistent and

	To be consistent means that the architecture does not do the same or
similar things in mutually incompatible ways, that it is not
self-contradictory. If a service is invoked to provide a stock quote using
an XQL query in one place, it should do so everywhere throughout the system
in the same manner. There should not be wildly different means to achieve
the same ends in the architecture.

	To be coherent means that the architectural components work together
to form a logical whole. The dictionary does a good job with this word:


a) Marked by an orderly, logical, and aesthetically consistent relation of

b)Composed of mutually dependent parts; making a logical whole; consistent;
as, a coherent plan, argument, or discourse.

	Hopefully this clarifies things.



> -----Original Message-----
> From: Timothy N. Jones [mailto:tim@crossweave.com]
> Sent: Tuesday, March 12, 2002 12:10 PM
> To: www-ws-arch@w3.org
> Subject: D-AG0008: "is coherent and consistent in its definition"
> Goal 8 of the web services architecture is stated as follows:
> 	"is coherent and consistent in its definition"
> Following Daniel's lead, we have two questions to ask of this goal:
> 1. Is the proposed text above sufficiently clear, concise and 
> intelligible
> to serve its purpose?
> 2. What are the critical success factors that we need to 
> achieve this goal?
> The only issue I have regarding the wording is whether we should add
> something to the effect that the architecture shall be "complete" or
> "self-contained" -- when we look at the use cases for web 
> services, any
> technologies required to implement them should be part of the 
> architecture.
> I believe that simplicity is a part of coherency, but there 
> is a separate
> goal (D-AG0005) for that, so I don't think it needs further 
> elaboration
> here.
> Regarding CSFs, I believe that a visualization in the form of a two
> dimensional diagram of the architectural components and the 
> relationships
> between them is a top-level CSF.  This would preferably be a simple
> "stack"-type picture that could be understood by a wide 
> audience, rather
> than something more formal such as a UML class diagram.
> The only quantitative metrics that come to mind are from the 
> OOAD world and
> focus on simplicity, so I don't think they belong in this 
> goal.  I have
> mentioned one qualitative metric for completeness above.  
> Other questions
> that come to mind are:
> "Does the architecture support the concepts used in commonly 
> accepted design
> patterns?" [coherency]
> "Is there a small number (preferably one) way that a given set of
> architecural components may be combined to achieve a particular
> functionality." [consistency]
> Please share any comments regarding the wording of this goal 
> and appropriate
> CSFs.
> Cheers,
> Tim
Received on Friday, 22 March 2002 18:23:03 UTC

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