Re: [xml-dev] RE: Caution using XML Schema backward- or forward-compatib

["Stephen Green" <stephengreenubl@gmail.com>]

I'm thinking of something along either of these lines:
Plan (A):
Just as there are advocates of dual purpose urls for semantic web
- a single url which the server detects as being called by human or
by machine and returns either the human-readable content or the
machine-readable metadata (e.g. RDF/S) accordingly, so I would
envisage a special case, perhaps, for WSDL. There might be an
HTTP header attribute, say, that says 'give me WSDL' and another
which say (perhaps in the same header) 'I can also understand
RDF/S' (or OWL-DS or OWL-Lite, say). The semantically equipped
server might return WSDL (or even SOAP at runtime) along with,
perhaps in the HTTP header (until WSDL/SOAP acquire the right
semantics, say), a pointer to a semantic metadata resource or
somehow the resource itself. That resource might be like this

RDF/S classes and properties
RDF/S descriptions - perhaps 'graphs' of endpoint + XPath + metadata
                             - perhaps a pointer to or inclusion of Schematron
                               or OWL or genericode (for, say, code values)
With some kind of profile or ontology limiting all this for web service
capabilities (perhaps one for WSDL/design time and another for SOAP
/runtime) similar order of complexity to Dublin Core, say, it should
be (am I wrong?) feasible to have tools detect semantic changes
such as the addition of a new code value so the consuming software
'knows' to look out for it or throw an error if it can't handle new codes.
Phew! Sorry for long sentences (no time for shorter ones!).

Plan (B): use BPSS with CPPA - ingredients already there in standards
- just add software.

In both cases, I don't know enough about it but maybe a semantic
reasoner is needed. So combine knowledgebase and WS software
and some kind of profile and special stuff on servers for HTTP.

Plan (C): find something like this but doable now, e.g. just using
WSDL + SOAP + XML Schema + Schematron and some codelists
defined in Schematron with a way to interpret new code values (like
UBL proposes) without breaking anything (using XSLT to trim stuff
not understood too).

Plan (D): extend both WSDL and SOAP to include a url to a particular
type of RDF or OWL or Schematron metadata file
(e.g. with codes/values) which can be updated at any time without
new schema or new url - where updates can be detected by equipped
consumer software if need be and exceptions or appropriate action
taken.

On 04/01/2008, Fraser Goffin <goffinf@googlemail.com> wrote:
> > - each specifying within the WSDL the meaning of the distance
>
> What mechanism in WSDL are you expecting to be able to define semantics ?
>
> Accepting the idea that it might be possible to define schemata that
> provide sufficient meta-data to ensure that semantics are [less]
> ambiguous (i.e. your idea that the introduction of the 'method'
> attribute') is fair enough, but we also need to consider the case that
> Michael [Kay] outlined, that of 'semantic drift'. An information item
> that starts out with one purpose and over time drifts into other uses,
> and of course that very often we don't create a perfect schema in
> version 1.0 with all future needs catered for :-)
>
> As far as the approach of creating a new URL for what in some cases
> should be considered as minor revision changes (note: I don't include
> a semantic change as one of those), I agree, this seems to be an
> un-necessary overhead. Thats why I prefer to categorize changes as
> breaking and non-breaking where non-breaking should provide at least
> backwards compatibility and ideally forwards as well.
>
> Fraser.
>
> On 04/01/2008, Stephen Green <stephengreenubl@gmail.com> wrote:
> > > Not using a codelist but using a method attribute seems to solve
> > > the problem with no need for new url. That seems to be the key.
> > > Add metadata everywhere in version 1. I still wonder: Is RDF/S
> > > going to be a valid way to do this? Would it work? It does seem
> > > to be becoming the standard way to add metadata for semantics.
> > >
> > P.S.
> >
> > With example
> > <distance>100</distance>
> > what meaning does this have? If it isn't clear what distance is meant
> > then maybe there is a need for *two* new web services:
> > - each specifying within the WSDL the meaning of the distance
> > - one for the first meaning and another for the second
> > - both being a distinct improvement on the first
> > - the original being preserved for consumer compatibility where
> >   an attribute like 'method' might break the WSDL consumers
> > This just isn't likely to happen though because there might be
> > all sorts of similarly vague elements throughout the WSDL, each
> > perhaps needing new versions at some point - and a new url
> > or several new urls for each case just doesn't seem acceptable.
> >
> > Maybe if the attribute was not added in the first place then there
> > is a way to add the metadata it would have contained in another
> > way which doesn't break the WSDL consumers. The missing
> > piece seems to me to be 'tool support'.
> >
> > Maybe if OWL were used to add the metadata (as an afterthought
> > if an attribute like 'method' was missed from version 1) there might
> > be a way for a change in such metadata to trigger a signal in the
> > web service consumer. Perhaps that needs to be added to tools
> > and maybe standardization is needed too. I would love to be on the
> > committee deciding what to call any possible extension of WSDL
> > or combination of WSDL and OWL say - maybe there is a way
> > to call it WSDL-OWL and switch letters to make it WS-LD-OWL,
> > pronounced 'wise-old-owl' :-)
> >
> > I don't know enough about WSDL but when working with ebXML
> > I asked for an attribute 'externalDocumentDefRef' to be added to
> > ebXML BPSS. This, were there the tool support, could perhaps
> > allow a pointer to semantic metadata to be linked to a web service
> > via CPP/A and ebBP definitions. I would think tools would have to
> > detect any changes in the metadata and signal that something has
> > to be looked into as a thrown exception (fatal or otherwise). So
> > with the right ingredients in the web service, it is possible for
> > semantic changes to be automatically picked up by suitable tools.
> >
> > --
> > Stephen Green
> >
> > Partner
> > SystML, http://www.systml.co.uk
> > Tel: +44 (0) 117 9541606
> >
> > http://www.biblegateway.com/passage/?search=matthew+22:37 .. and voice
> >
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>


-- 
Stephen Green

Partner
SystML, http://www.systml.co.uk
Tel: +44 (0) 117 9541606

http://www.biblegateway.com/passage/?search=matthew+22:37 .. and voice