Object-oriented serialization (Was Re: Some questions)
W. E. Perry
wperry at fiduciary.com
Mon Dec 6 05:58:20 GMT 1999
Ah, but the nuts and bolts of specific *behaviour* over links will have to be defined,
ultimately as procedural code of some sort, in some generally invocable form. The logic (case,
sequential, conditional) leading to the code which implements that behaviour might well--and
probably ought to be--expressed as XML text, but at some point, from a leaf node of an XML
document expressing a decision tree, it will be necessary to invoke procedural code to
implement a defined behaviour. That procedural code might--and probably ought to
be--parameterized by XML and designed to return XML, but of itself, as procedural code, it is
opaque to the XML which invokes it. That procedural code, implementing a specific behaviour,
is the 'class of resource' which you are looking for (as its opacity to the instance
demonstrates). The behaviour expressed in that procedural code is invoked via a particular
URI, but a unique process is instantiated only in the scope and context of the current
document, and presumably only through parameterization specific to the instance, passed to
generally available code. In fact, anything which might reasonably be described as behaviour
is generally available to XML processing only as a 'class of resource': that generally
available class must not be confused with its particular instantiation, for an instance
invocation of that behaviour via a particular URI does not impair the availability of that
URI--and of the behaviour it addresses--to other invocations from different contexts.
Rick Jelliffe wrote:
> Yes, except XLinks are specified in instances, not as a schema per se.
> I hope the XML Schema will have some extension mechanism to
> allow these kinds of thing, but who knows.
> It is true that sequence and containment relations between elements
> in a content model could be treated of as some kind of extended link.
> And we cannot use hrefs to the instances because we don't know
> what the instance document URI is: a URI identifies a particular
> resource not a class of resources. XLinks are not designed for
> us as schema declarations.
> So I think there needs to be first-class support for this in the
> schema language itself: in the case of XML Schemas, probably
> the most possible thing would be a role attribute (or some equivalent)
> on groups.
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