W3C home > Mailing lists > Public > xmlschema-dev@w3.org > July 2001

RE: Missing WSDL Schema

From: <Noah_Mendelsohn@lotus.com>
Date: Sat, 14 Jul 2001 22:22:22 -0400
To: Martin Duerst <duerst@w3.org>
Cc: "'Julian Reschke'" <julian.reschke@gmx.de>, Michael Brennan <Michael_Brennan@Allegis.com>, Pradyumna_Siddhartha <Pradyumna_Siddhartha@infy.com>, xmlschema-dev@w3.org
Message-ID: <OF09C5CD19.E9A7D7CD-ON85256A8A.000B7114@lotus.com>
This is drifting into a rehash of the oft-visited question of what, if 
anything should be at "the end" of a namespace URI reference.   I suspect 
we don't want to reopen the whole debate again, but for what it's worth, 
one of the main problems that was discussed when we considered the issue 
during design of schemas had to do with the timeouts that can occur when a 
namespace does not, in fact, have a schema at all.  If you require that 
schema-aware processors always attempt to dereference a NS URI to get 
anything (RDDL, schema, etc.), then if there is any chance that such a 
resource is not there, most network systems incur quite a delay.  This 
problem was reported by a vendor who had operational experience with 
deployed systems that used earlier schema systems and a convention of 
derferenceing the URI; they found the performance problems and timeouts to 
be unacceptable.

Of course, in situations where you are reasonably sure that a resource 
will be available (cached or otherwise), doing a dereference to get it can 
be a wonderful strategy.  Those are among the reaons why we (a) decided to 
build an architecture that would support the development of conventions, 
such as RDDL, for locating schemas from a NS URI but (b) stopped short of 
requiring that processors attempt the dereference.   Also, there are 
situations in which the application consuming a document cannot trust the 
instance author to supply an appropriate schema.  For these circumstances, 
processors can be built to accept schemas from the consuming application 
or other sources -- of course, it is possible also to build processors 
that derefence the NS URI, check the schema retrieved to make sure it is 
indeed the one intended, and thus ensure that producer and consumer had a 
consistent presumption regarding the schema.   The schema recommendation 
does not standardize such behavior, but does not preclude its 
implementation either in particular processors, or in some layered 
standard to be issued in the future.  Such a standard could mandate, for 
example, the use of RDDL.

So, while we know from past debates that not everyone agrees on what is 
desireable or whether the decisions made by the schema WG were indeed what 
one person or another would have preferred, I think the above does 
summarize some of the issues we considered and the intended behavior of 
the schema recommendation.  Hope this is helpful in the current discussion 
of WSDL.  Thanks.

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Noah Mendelsohn                                    Voice: 1-617-693-4036
Lotus Development Corp.                            Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
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Received on Saturday, 14 July 2001 22:24:49 GMT

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