Inheritance in XML

[Peter Murray-Rust]

It is clear that we are at a key stage in developing these areas, and I
think we have a shortage of good software to help us. I'd like to see if
there are simple communal ways forward.

Concentrating on the semantics of DTDs and document instances (i.e. not the
interpretation of the spec), it seems that we have (at least) the following
toolset:

- adding semantic information to the DTD. This would give per-element and
per-attribute prose. Unfortunately this is not defined in SGML or XML DTDs
- only comments are allowed, and there is no standard for their creation.
This makes it extremely difficult (say) even to generate toolTips for the
semantics of ELEMENTs. I find this frustrating and potentially quite easily
avoidable. For example the idea of recasting the DTD in XML (which I have
re-posted recently) allows (at least) Xlink-annotation and possibly formal
extensions through XML.

- Allowing for semantic information to be added at document authoring time
(or later). Thus CML/TecML uses constructs such as <ITEM
TITLE="phlogistonCount"
HREF="http://www.vhg.co.uk/some/hyperglossary.xml#phlogiston">...</ITEM> to
categorise quantities and allow full semantic resolution through
distributed terminology. [We shall announce the hyperglossary concept and
its DTD very shortly.]

- linking ELEMENTs to software (i.e. behaviour). This can either be done on
an implicit basis (e.g. CML:MOL links to jumbo.cml.MOLNode probably through
xml:namespace pointers) or through the stylesheet syntax (which we await -
I very much hope it has the ability to embed Java methods).
	Note that *I* would often classify this as 'semantics' because it is often
easier to define technical operations in terms of machine-based rules or
specifications rather than prose. As an example, 'electronegativity' might
be defined by an algorithm rather than prose.

Whether rendering (by stylesheets) adds semantic information will depend to
some extend on the culture and experience of the readers. This has so far
appeared to be the most prominent way of 'adding semantics'; I'd like to
see some support for the others mentioned here.

	P.
  
Peter Murray-Rust, Director Virtual School of Molecular Sciences, domestic
net connection
VSMS http://www.nottingham.ac.uk/vsms, Virtual Hyperglossary
http://www.venus.co.uk/vhg

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