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   Re: Why the Infoset?

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  • From: John Cowan <cowan@locke.ccil.org>
  • To: abrahams@acm.org
  • Date: Mon, 31 Jul 2000 00:05:27 -0400 (EDT)

On Fri, 28 Jul 2000, Paul W. Abrahams wrote:

> Couldn't the effect of
>   <myinclude xinclude:href="something.xml"/>
> have been described in terms of XML textual forms rather than in terms of the
> Infoset?  In other words, was the choice of the Infoset as the descriptive
> mechanism logically necessary or just more convenient?

More convenient, certainly.  Whatever is done in Infoset terms could
be done in textual terms as well, but with more pain.  For example,
it would be necessary to prescribe:

	that either double quotes or single quotes could be used;
	that the whole element could be replaced by an entity reference;
	that the attribute value could be replaced by an entity reference;
	that the element could have an adjacent start-tag and end-tag
		rather than an empty-element-tag;
	that any or all of the characters in the attribute value could
		be replaced by character references;
	that the "xinclude:" prefix could be replaced by another prefix,
		provided the Namespaces rules are obeyed;
	that all the whitespace could be expanded;

and perhaps other flexibilities as well.  Without the infoset,
all of this typically winds up being carried by covering words
(as in RDF Model & Syntax) that "all XML flexibilities apply" or the like.
The Infoset allows us to distinguish between essential and accidental

> Viewed as an elegant description of the information contained in an XML
> document, the Infoset make sense.  But unlike the other XML specs, its
> normative effect is unclear.  If I'm implementing an XML-related processor of
> any variety, what does the Infoset require me to do that I would not have to do
> if the Infoset never existed?

Undoubtedly the Infoset is more useful when writing specifications rather
than implementations.  This is true both of the kind of generalized
specifications that the W3C and other groups produce, and of the kind
we usually call "program documentation".  Rather than documenting exactly
what your parser provides to applications, it suffices to say that
it provides the Infoset core, e.g.  (You still have to document just
how it provides the core, of course.)

John Cowan                                   cowan@ccil.org
C'est la` pourtant que se livre le sens du dire, de ce que, s'y conjuguant
le nyania qui bruit des sexes en compagnie, il supplee a ce qu'entre eux,
de rapport nyait pas.               -- Jacques Lacan, "L'Etourdit"


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