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Re: Issue 29: Exist non-serialisable data models?

From: Dan Brickley <danbri@w3.org>
Date: Fri, 12 Oct 2001 01:33:40 -0400 (EDT)
To: Paul Cotton <pcotton@microsoft.com>
cc: "W3C XML Protocol IG (E-mail)" <xml-dist-app@w3.org>, <connolly@w3.org>, <em@w3.org>, <brian_mcbride@hp.com>, <swick@w3.org>
Message-ID: <Pine.LNX.4.30.0110120038090.24437-100000@tux.w3.org>

Hi Paul,


On Thu, 11 Oct 2001, Paul Cotton wrote:

> Issue 29: "Exist non-serialisable data models?" from [1] implies that
> there _might_ be data models that cannot be encoded using the SOAP 1.2
> data model.
>
> When this issue was created I suggested [2] that it was
> only a true issue if someone could bring forward such a non-serialisable
> data model.  I would like to propose we now close this issue (with no
> further action) based on the following resolution text:
>
> "The current SOAP/1.2 model is capable of representing directed graphs as
> well as object graphs and enables a recipient to deserialize an XML
> instance to recreate those graphs. It is not clear whether there are
> other data models that potentially are interesting to serialize but not
> representable within the SOAP data model.  Since no examples of
> non-serialisable data models have been brought to the attention of the
> XML Protocol WG, it is proposed to resolve this issue with no further
> changes to SOAP 1.2."


This is premature!. All the while the SOAP/1.2 spec sports a section "The
SOAP Data Model[3] that is yet to be written, you cannot reasonably close
this issue by saying "nobody failed to map to our model". Right now, the
latest SOAP Working Draft says, under Data Model:

	"This section is the placeholder for the description of the SOAP data
	model".

The XML Protocol WG charter[4] explicitly calls out (s1.4) two particular
information models, RDF and UML. I don't know much about the UML/SOAP
relationship, but I've been looking out for opportunities to map RDF into
SOAP.

You propose to move directly from the current Issue 29 text,

	"The current SOAP/1.1 model seems to be capable of representing
	directed graphs as well as object graphs [...]"

...to closure of this issue w.r.t. SOAP 1.2. I suggest we
wait until a version of 1.2 has been published that includes a
specification of the SOAP Data Model. Currently, the SOAP Data Model is
not explicitly articulated, but is described rather indirectly through a
rather narrative account of the serialized form given in section
4 of the specification. This makes it hard for other groups reviewing SOAP 1.2 to
assess the expressivity of the SOAP data model, or to say with any
confidence that SOAP can, or cannot, adequately encode their data model.

I appreciate the need to finalise a SOAP 1.2 specification asap, and that
there may be other reasons to leave some aspects of the encoding/serialization
work to future efforts. Nevertheless, I really don't think the current
proposed closure is appropriate at this stage. My particular concern here
is the importance of keeping W3C's RDF work alligned with mainstream
developments in the XML world, notably SOAP. RDF was, per [3], brought to
the attention of the Protocols WG from the start, and makes a fine test
case for the closure of Issue 29. I have been looking forward to the day when I
can point RDF implementors at a maturing SOAP spec
and say "here's the SOAP data model; here's a suite of SOAP test
cases; do these map to/from RDF?". I don't believe we're at that stage
yet, and that consequently it is too early to say that

	..."no examples of non-serialisable data models have been
	brought to the attention of the XML Protocol WG".


The RDF community has been living with a W3C REC (the '99 RDF Model
and Syntax spec) that did not adequately distinguish between an abstract
information model and its particular default XML encoding. For RDF, this caused
significant problems for users of the spec, which we are now addressing
through a reformulation of the RDF syntax spec[5], through a more formal
and mathematical account of our underlying model[6], and through a set of
test cases that guide our discussions[7]. My understanding is that the
SOAP 1.2 spec is taking a similar turn: a re-articulation of the SOAP
Data Model, (also too the account of serialization rules?), and I believe
working towards a SOAP test suite? If so, these efforts have more in
common with the RDF Work than some might have expected.


I didn't mean to write such a long note, just really wanted to pop up and
say "please don't close this issue before publishing a description of the
SOAP data model". When that's done, I will take care (via the W3C XML and
S.W. CGs) to make sure the spec gets a careful review from
the RDF community, particularly regarding the ability to round-trip RDF
data graphs through a SOAP representation.

best wishes,

danbri



[3] http://www.w3.org/TR/soap12-part2/#datamodel
[4] http://www.w3.org/2000/09/XML-Protocol-Charter#scope
[5] http://www.w3.org/TR/rdf-syntax-grammar/
[6] http://www.w3.org/TR/rdf-mt/
[7] http://www.w3.org/TR/rdf-testcases/

> /paulc
>
> [1] http://www.w3.org/2000/xp/Group/xmlp-issues.html#x29
> [2] http://lists.w3.org/Archives/Public/xml-dist-app/2001Feb/0045.html
>
> Paul Cotton, Microsoft Canada
> 17 Eleanor Drive, Nepean, Ontario K2E 6A3
> Tel: (613) 225-5445 Fax: (425) 936-7329
> <mailto:pcotton@microsoft.com>
>
>
Received on Friday, 12 October 2001 01:33:44 GMT

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