In Search of XML Interoperability: XLink + XML Schema = Inte roperability?

[Michael Rossi]

   This is long, sorry. But it covers a lot.

In search of the holy grail, Roger L. Costello wrote:
> 
>    XML Interoperability: the ability of an application to 
> make effective use of an XML document that it receives.  

   OK.

> There are two ends of the XML Interoperability spectrum:
> [1] At one end of the spectrum an application is coded for a specific
> schema and this is able to make effective use of only XML documents that
> conform to that schema.
> [2] At the other end of the spectrum the application is able to make
> effective use of any XML document that it receives, regardless of the
> schema that the XML document conforms to.

   Key word in [2] is _any_. Possibly to ambitious for starters, walk before
you run and all that.

> I contend that [2] is the desired goal, but [1] is where we are at
> currently.  So, how do we get to [2]?  That's what I wish to explore.
> 
> Question.
> If an application receives an XML document that conforms to a schema for
> which the application has no familiarity, how does the application "make
> effective use" of it?
> 
> Answer.
> From my own life, when I am exposed to a new idea I learn best by
> relating the new idea to something that I already know.  Similarly, if
> an application receives an XML document that contains new, unfamiliar
> elements/attributes then it may be able to still make use of them (the
> unfamiliar elements/attributes) if it can relate them to
> elements/attributes that it knows about.
> <snip/>
> 
> So, what are the key components of XML Interoperability?  There are two
> components:
> (1) Describing Relationships: 
> <snip/>
> (2) Discovering Relationships:
> <snip/>

   Actually, I think there's more to it than that. Not only do we as humans
come to know what things are based on their context, similar past experience
(relationships), etc., but in order to "make effective use" of them we need
to have lots of supplementary information (that we usually take for
granted).

   Also, in order for computers to make effective use of information they
must (as we all know) be programmed very specifically to take the
appropriate action based on given input. For this reason, I believe that not
only does an application need to be able to "accept" a given term, but it
must be able to locate some programmed action to be taken based on that
input.

   There are lots of different ways to approach this goal. The Biztalk
approach (maybe XML.org as well) seems to want to provide a database
something like (but not quite exactly) your relationship database, with the
idea being that once you've made everything accessible you can
straightforwardly map from one vocabulary to another, and maybe process
information based on those mappings instead of the raw input.

   Another approach is that of the ontologies, wishing to define fundamental
concepts which can then hopefully be extrapolated to develop meaningful
processing reagrdless of what terms lie on top of the concepts.

   Another approach might involve some extension/usage of AI or NLP
paradigms. Myself, I've wondered if something like JXML's Coins (which I
haven't had time to investigate) might be suitable for "attaching" code to
data. I also recall seeing something out of Netscape about "action sheets",
which seems to describe this thought.

   This list has also discussed at times the topic of how to give meaning to
data (I believe this was an extension of the 'XML Schema adding semantics
above syntax' threads). Unfortunately, much of the thought behind this
problem to date has been largely theoretical and has done little to prove
any practical application of the ideas. I'm glad you raised this again
Roger, because we'll never get from point [1] to point [2] unless a fairly
simple, generic approach to attaching processing to data can be developed
and accepted. XML has opened the door to interoperability, but we're a long
way from being able to cross the threshold.

<snip topic="XLink and relationships"/>

Michael A. Rossi
mailto:mrossi at jcals.csc.com
856-983-4400 x4911

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