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

From: Dan Brickley <danbri@w3.org>
Date: Tue, 16 Oct 2001 22:25:18 -0400 (EDT)
To: Andrew Layman <andrewl@microsoft.com>
cc: <Noah_Mendelsohn@lotus.com>, "Hutchison, Nigel" <Nigel.Hutchison@softwareag.com>, <jacek@idoox.com>, <xml-dist-app@w3.org>
Message-ID: <Pine.LNX.4.30.0110162224450.32379-100000@tux.w3.org>

What is a "DLG schema"?

Dan

On Tue, 16 Oct 2001, Andrew Layman wrote:

> We are using in a limited way the ID mechanism in section 5.  The SOAP
> encoding rules allow us to convert from a DLG instance plus DLG schema
> to XML syntax plus XML schema; they also allow the reverse translation.
> The reference to ID indicates that in such a produced XML schema, the
> "id" attribute should be of type ID.  However, the conversion from an
> XML instance to a DLG instance is determined by the DLG schema, not the
> XML schema.  Hence, it is true but not a problem that, as Asir notes,
> the schema information, if any, that asserts the ID type is not used
> during XML to DLG conversion.
>
> -----Original Message-----
> From: Noah_Mendelsohn@lotus.com [mailto:Noah_Mendelsohn@lotus.com]
> Sent: Tuesday, October 16, 2001 2:03 PM
> To: Hutchison, Nigel
> Cc: danbri@w3.org; jacek@idoox.com; xml-dist-app@w3.org
> Subject: RE: Issue 29: Exist non-serialisable data models?
>
> There are limitations on the XML that can be within a SOAP envelope.  No
>
> PI's, no user-defined entities (no internal subset DTD), and although
> there have been some very useful points made by Asir that suggest we
> aren't really using the XML ID mechanism, in practice (because XML only
> knows about ID types when DTDs are processed, and we don't have 'em)
> it's
> probably a mistake to duplicate an ID values between the contents of
> your
> data and any ID's used in other header entries.
>
> ------------------------------------------------------------------------
> Noah Mendelsohn                                    Voice: 1-617-693-4036
> Lotus Development Corp.                            Fax: 1-617-693-8676
> One Rogers Street
> Cambridge, MA 02142
> ------------------------------------------------------------------------
>
>
>
>
>
>
>
> "Hutchison, Nigel" <Nigel.Hutchison@softwareag.com>
> Sent by: xml-dist-app-request@w3.org
> 10/16/01 12:56 PM
>
>
>         To:     "'Jacek Kopecky'" <jacek@idoox.com>, danbri@w3.org
>         cc:     xml-dist-app@w3.org, (bcc: Noah Mendelsohn/CAM/Lotus)
>         Subject:        RE: Issue 29: Exist non-serialisable data
> models?
>
> Jacek,
>
> Supposing a Soap message carried a query(say X-Query) to an XML Database
>
> and
> the database sent back a response
> representing a node set as a serialized XML document. Would all possible
> responses be encodeable as a SOAP data model?
> I think not - unless it was a severely crippled XML Database.
>
> But it seems like a reasonable requirement. In fact users have asked for
>
> it.
>
> Does this support your case?
>
> Nigel W.O Hutchison
> Chief Scientist
> Software AG
> Uhlandstr 12,D-64297 Darmstadt, Germany
> +49 6151 92 1207
>
>
>
>
> -----Original Message-----
> From: Jacek Kopecky [mailto:jacek@idoox.com]
> Sent: Tuesday, October 16, 2001 6:02 PM
> To: danbri@w3.org
> Cc: xml-dist-app@w3.org
> Subject: Re: Issue 29: Exist non-serialisable data models?
>
>
>  Dan,
>
>  You seem to assume that data passed in SOAP messages must
> follow the SOAP data model and be encoded using the SOAP encoding
> rules. Neither is true, please read on.
>
>  As SOAP (as specified in [3], without the Adjuncts) is a
> messaging protocol, it can carry any data serialized into XML.
> >From the point of view of the core SOAP, the serialization rules
> are application-dependent.
>
>  SOAP provides a mechanism for specifying the encoding rules used
> for serialization of the data contained in a message - the
> encodingStyle attribute information item (see [1]). A specified
> encodingStyle implicitly specifes also the data model.
>
>  Requirement R402 (and the issue #29 resulting from it) says that
> SOAP must be able to serialize data in data models not directly
> representable by XML Schema (which would be a tree data model).
> It explicitly mentions the object graph data model.
>
>  SOAP specifies a serialization of one data model, and that would
> be sections 4 and 3 of Adjuncts [2], so that any data following
> this data model, which is prevalent e.g. in RPC applications, can
> be serialized in a common way. I agree the data model section is
> yet to be written.
>
>  In case an application's data follows the data model from
> section 3, it may be serialized using the encoding rules from
> section 4.
>
>  In case an application's data (like RDF, for example) doesn't
> map naturally onto our data model, the application can use its
> own serialization rules, which can follow some already existing
> specification. Applications wishing to communicate RDF data only
> need to agree on a URI that would identify the RDF XML
> representation, and use that as the encodingStyle attribute
> information item's value. The serialized form would then follow
> the already existing RDF XML representation.
>
>  So I think the right resolution to issue #29 would be:
>
>  "SOAP specifies how to encode data from the object-graph data
> model. SOAP also allows the encoding of other data models
> representable in XML using custom encoding rules identified in
> the encodingStyla attribute information item in a message.
> Therefore no data models exist that are serializable to XML but
> not serializable to SOAP."
>
>                             Jacek Kopecky
>
>                             Idoox
>                             http://www.idoox.com/
>
> [1] http://www.w3.org/TR/2001/WD-soap12-part1-20011002/#soapencattr
> [2] http://www.w3.org/TR/2001/WD-soap12-part2-20011002/
> [3] http://www.w3.org/TR/2001/WD-soap12-part1-20011002/
>
>
>
> On Fri, 12 Oct 2001, Dan Brickley wrote:
>
>  >
>  > 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/
>  >
>
>
>
>
Received on Tuesday, 16 October 2001 22:25:22 GMT

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