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RE: Reference requirements

From: Anne Thomas Manes <anne@manes.net>
Date: Tue, 19 Feb 2002 10:30:24 -0500
To: "Paul Prescod" <paul@prescod.net>, <www-ws-desc@w3.org>
Message-ID: <CJEIKEMEBAONGDDNLEKFMEAGDMAA.anne@manes.net>
Systinet WASP supports remote references using a header element to reference
the instance id.

Anne Thomas Manes
CTO, Systinet

> -----Original Message-----
> From: www-ws-desc-request@w3.org [mailto:www-ws-desc-request@w3.org]On
> Behalf Of Paul Prescod
> Sent: Tuesday, February 19, 2002 6:38 AM
> To: www-ws-desc@w3.org
> Subject: Reference requirements
>
>
> "Sadiq, Waqar" wrote:
> >
> > Ok.  I think I get it and sorry for not reading it like that.
> In a sense
> > that is also a requirement on the web services architecture
> work group that
> > the web services should be able to support references.  For
> example, if I am
> > not wrong, I think XMLP does not address specifying object
> references and
> > how they can be passed back.  Would the underlying protocols
> have to support
> > passing objects by reference before a description language can
> express it
> > properly?
>
> Well, yes, I think that SOAP is somewhat broken in this respect also.
>
> But one can always pass a URI through SOAP so you can hack object
> references. SOAP doesn't help you but it doesn't prevent you from
> doing it either.
>
> Once you have a URI, SOAP will not prevent you from calling methods on
> the URIs that you retrieve as SOAP endpoints. Once again, SOAP doesn't
> help you but it doesn't get in your way. (Most SOAP toolkits might get
> in your way but that's a different issue).
>
> But if WSDL does not let you describe the resulting service then you
> really cannot realistically deploy it in a statically-typed programming
> world. So it becomes quite hard to do anything beyond getStockQuote. ;)
>
> All real web services need to deal with state somehow. Delegating that
> to the application layer is a cop-out. WSDL is where the rubber will hit
> the road. The cop-out will actually get in the way of people doing their
> jobs and solving real-world problems.
>
> Consider the following use-case, call it UC0666 if you like:
>
> I have many components that accept some kind of business document. All
> of these business documents have certain common behaviors and in
> particular they may be cancelled, approved or postponed. It must be
> possible for one component (let's say the purchasing interface) to
> report the existence of a document to another component (let's say the
> purchasing approval workflow engine). The purchasing approval component
> must be able to invoke the "cancel", "approve" or "postpone" methods on
> the business document.
>
> Of course in simple cases one can always work around the lack of
> references by passing around magic cookies to some kind of "purchase
> order manager" but this scales very poorly because it means that ALL
> access to purchase orders throughout the entire company must go through
> a single component, just because it happens to implement the
> cancel_based_on_cookie(), approve_based_on_cookie() and
> postpone_based_on_cookie methods.
>
> In programming terms the right way to do it is:
>
> interface po:
>    def approve():
>       (do some authorization etc. and then change the state to cancel)
>
>    def cancel():
>       (do some authorization etc. and then change the state to cancel)
>
>    def postpone():
>       (do some authorization etc. and then change the state to cancel)
>
> class purchasing_interface_1:
>     def accept_purchase_order(address, items, etc. etc.):
>         validate(address, items, etc. etc.)
>         po = new PO(address, items, etc. etc.)
>         my_list_of_purchase_orders.add(po)
>         approval_engine.add(po)
>         return po
>
> class purchasing_interface_2:
>     # same basic thing but owned by different part of organization
>     def our_accept_purchase_order(address, items, etc. etc.):
>         validate(address, items, etc. etc.)
>         po = new PO(address, items, etc. etc.)
>         my_list_of_purchase_orders.add(po)
>         approval_engine.add(po)
>         return po
>
>
> class approval_workflow_component:
>     def ceo_says_approve(po):
>         po.approve()
>
> In programming terms the wrong way to do it is:
>
> class po_manager:
>    def new_po(address, item, etc.):
>        cookie = make_new_cookie()
>        my_list_of_purchase_orders.add(cookie, address, item)
>        return cookie
>
>    def approve(cookie):
>       (do some authorization etc. and then change the state to cancel)
>
>    def cancel(cookie):
>       (do some authorization etc. and then change the state to cancel)
>
>    def postpone(cookie):
>       (do some authorization etc. and then change the state to cancel)
>
> class purchasing_interface_1:
>     def accept_purchase_order(address, items, etc. etc.):
>         validate(address, items, etc. etc.)
>         po_cookie = global_po_manager.new_po(address,item, etc.)
>         approval_engine.add(po)
>         return po_cookie
>
> class purchasing_interface_2:
>     def accept_purchase_order(address, items, etc. etc.):
>         validate(address, items, etc. etc.)
>         po_cookie = global_po_manager.new_po(address,item, etc.)
>         approval_engine.add(po)
>         return po_cookie
>
> class approval_workflow_component:
>     def ceo_says_approve(cookie):
>         global_po_manager.approve(cookie)
>
> Note how instead of just specifying the interface to purchase orders I
> had to centralize everything through a single component that implemented
> that interface for purchase orders from different parts of the company
> that might not otherwise have had to be centralized. The centralization
> decision should be a business decision and not forced by the weaknesses
> of the description language.
>
> WSDL needs to be able to define the abstract "purchase order" interface
> and to describe methods like accept_purchase_order which return objects
> of that type. At the SOAP level those would be URIs to dynamically
> created endpoints representing those purchase orders.
>
>  Paul Prescod
>
Received on Tuesday, 19 February 2002 10:30:33 GMT

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