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RE: D-AG0007.1- defining reliable and stable WS [was RE: Status: D-A G0007 - reliable, stable, predictable evolution]

From: Mark Potts <mark.potts@talkingblocks.com>
Date: Wed, 20 Mar 2002 15:51:58 -0800
To: "'Hugo Haas'" <hugo@w3.org>, <www-ws-arch@w3.org>
Message-ID: <006001c1d06a$39b616b0$9a68fea9@talkingblocks.com>
Hugo... Forgive me if some of this has been covered, I couldn't see that it
had though.

Not sure if I agree with the definition of "predictable evolvable" and its
correlation to Stability. In the Architecture who is responsible for knowing
the consumers of a service and managing the notification of detrimental
change? I would not say that notifying a consumer at the time of invocation
that the service has changed would not constitute a stable system! Even
notifying them prior depends on the time you give them to react. This leads
me to believe someone else is responsible for managing this task.

I am presuming we are not advocating the service itself tracks its
consumers, such that it can notify them of detrimental change. So that means
a third party outside the producer and consumer. If this is true then I
would say "predictably evolvable" should include the ability of a Web
Service to define its compatibility ( i.e. its WSDL and the relationship it
has to other WSDL ), such that the third party can manage that relationship
and make services "predictable evolvable" not just from a consumers
perspective but a producers perspective also and thus more stable.

The case we need to be sure of is changes in WSDL that make the new
definition non-compatible with the last definition. In the case of WSDL
extending its port types, would I need to notify? or simply manage the
consumption in terms of service definitions.

Regards,
Mark Potts

> -----Original Message-----
> From: www-ws-arch-request@w3.org [mailto:www-ws-arch-request@w3.org]On
> Behalf Of Hugo Haas
> Sent: Wednesday, March 20, 2002 2:56 PM
> To: www-ws-arch@w3.org
> Subject: Re: D-AG0007.1- defining reliable and stable WS [was RE:
> Status: D-A G0007 - reliable, stable, predictable evolution]
>
>
> * Hugo Haas <hugo@w3.org> [2002-03-20 17:29-0500]
> > I am cathing up on lots of threads, no I will ask the following: has
> > "reliability, stability, and predictable evolution of [..] the
> > services themselves" been discussed?
>
> I am answering my own question:
>
>   http://lists.w3.org/Archives/Public/www-ws-arch/2002Mar/0309.html
>
> and following up on Suresh's email:
>
> * Damodaran, Suresh <Suresh_Damodaran@stercomm.com>
> [2002-03-18 16:58-0600]
> > I am considering the goal
> > "reliable, stable, and predictably evolvable web services"
> as D-AG0007.1
> > till we get a formal number for it. I volunteer to be the
> champion of this
> > goal
> > (unless somebody else (do you want to be?) wants it, that is:-)
> [..]
> > Stable - A WS is stable as long as any change in WS
> implementation conforms
> > to the independent specification (say WSDL) of the WS for
> all potential
> > users. Note that the specification of WSDL could change,
> and as long as all
> > users/service requesters are
> > "aware"/notified of it.
>
> This is where the "predictably evolvable" Web services meets
> stability, I think...
>
> [..]
> > -----Original Message-----
> > From: Hao He [mailto:Hao.He@thomson.com.au]
> > Sent: Thursday, March 14, 2002 6:35 PM
> > To: Damodaran, Suresh; Hao He; www-ws-arch@w3.org
> > Subject: RE: Status: D-AG0007 - reliable, stable,
> predictable evolution
> >
> >
> > hi, Damodaran,
> >
> > I would regard the stability of a web service as the
> stability of the
> > identifier (the URI) and the logic concepts associated with
> it. For example,
> > if a company sells car at http://xys.com/buy/car, one
> expects the URI to be
> > stable so one can bookmark this URI and one expect to buy a
> car not a book.
> >
> > <sd>
> > Would you not consider this a "reliability of URI" than a
> stability issue
> > in light of the discussion above?
> > </sd>
> >
> >
> > The second part is more tricky.  How about: "the
> architecture should enable
> > a web service to reveal its attributes to its consumers and verified
> > independently by its consumers or third parties so a
> selection mechanism can
> > be enforced. "?
> >
> >
> > Note the attributes can be more than just those needed in
> order to discover
> > the web service.
> > <sd>
> > We need a new goal for this (and a champion). Sounds fine to me.
> >
> > may be we need 2 - one for "discovery" and another for
> "criteria based
> > selection?"
> > </sd>
>
> ... and where it relates to the dependency on certain versions as I
> was talking about in my email[1].
>
> To me, the stability aspect is that the service will have a interface
> and behavior advertised for a particular version, which is I think in
> accordance with Suresh's definition.
>
> The predictability of evolution aspect hints that there is a way to
> say:
> - that one wants to use a particular version.
> - that a change in behavior and/or interface, in other words a change
>   of version, will be signaled one way or the other (a new URI for the
>   new version comes to mind, for example). This is what Suresh was
>   refering to with "Note that the specification of WSDL could change,
>   and as long as all users/service requesters are "aware"/notified of
>   it."
>
> I therefore support such a goal.
>
> Regards,
>
> Hugo
>
>   1. http://lists.w3.org/Archives/Public/www-ws-arch/2002Mar/0349.html
> --
> Hugo Haas - W3C
> mailto:hugo@w3.org - http://www.w3.org/People/Hugo/ -
> tel:+1-617-452-2092
>
>
>
Received on Wednesday, 20 March 2002 18:52:27 GMT

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