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   Re: Inheritance in XML (was Re: Problems parsing XML)

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  • From: Peter Murray-Rust <peter@ursus.demon.co.uk>
  • To: xml-dev@ic.ac.uk
  • Date: Fri, 17 Apr 1998 16:35:44

At 11:52 17/04/98 -0400, Frank Manola wrote:
>At 8:55 PM -0700 4/16/98, Tim Bray wrote:

>>>Markup doesn't care.  That's the beauty of it. :-

>>Yes! What he said.  As a result of having been a programmer since
>>A.D. 1979, my faith in interoperable APIs is torn and shredded.
>>But I think that interoperable syntax is usefully achievable.
>>Hence, XML. -T.

I support this - in a sense I have found that XML acts as a buffer between
different 'APIs'. It can hold the structure of the information and - if
necessary help support transformations where necessary. It also can relieve
the programmer of having to manage some of the structure. [As an example, I
hold me menu information in XML. When I wish to create a Java menu I can
translate that to the AWT/Swing commands whilst for some other system I can
translate it independently. OK - not everything matches precisely but it's
pretty good. Of course one can do it without XML - use an abstract
tree-based structure - but XML simply makes it natural the think this way.
Some of my XML 'code' never actually sees an angle bracket, but it's XML :-)

>These observations about the (at least so far) lack of success with truly
>interoperable APIs are certainly true, and the potential of interoperable
>syntax "feels" right, but I wonder to what extent we may be comparing
>apples and oranges here.  Specifically, what do we mean by "interoperable"?
>Interoperable APIs are hard at least in part because an incredible amount
>of semantics are (implicitly) built into a typical API (as is suggested by
>Matthew's comment).  Moreover, interoperable APIs are held to a "strict
>accountability":  the programs interacting through them must work without
>either syntactic or semantic errors (and, with programs, these are
>typically all bundled up).  However, if programs must agree on the precise
[.. and more useful stuff...]

I think the success of SAX (with complete credit to DavidM, of course) is -
in part - that the XML community has spent 10**4 email messages discussing
the semantics of what SAX operates on. So we all agree what Attributes,
Entities, etc are. [Imagine that someone just invented another language
with a different idea of 'entities' in and tried to interface it to XML
:-)].  This makes it possible to create an API where we are reasonably
happy about resolving semantics. Of course we'll need to make sure that the
implementations work harmoniously - there are still possible tweaks where
different implementers may take different directions (wh*t*sp*c*, etc.).
This will get harder with XLL and even tougher with RDF, etc. That's why I
think it's so important to work out these communal APIs and related

I shall revisit the DTD for DTDs in the near future because I think this is
a useful place where we all agree (I got that feedback from the list and
privately - I'll hack it next time I'm in the pub.).  I'd also very much
like to see implementation for some of the validity constraints (e.g. I'd
like to see Name validation which is straightforward but very easy to get
wrong or out-of-date.)

	Other suggestions for XML-DEV-based implementations/APIs where we all
'agree' on the semantics would be welcome.


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

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