Layering (was RE: Blueberry/Unicode/XML)

[Leigh Dodds <ldodds@ingenta.com>]

> -----Original Message-----
> From: Rick Jelliffe [mailto:ricko@allette.com.au]
> Sent: 10 July 2001 14:01
> To: xml-dev@lists.xml.org
> Subject: Re: Blueberry/Unicode/XML

[...Blueberry discussion elided...]

> ... I agree with James Clark that perhaps name checking (and
normalization) should be
> some kind of different layer to WF ultimately.

I've noticed a trend lately that many of the particularly thorny
issues that have been debated on XML-DEV result in the
identification, or suggested addition of a 'layer' within parsers and
beyond. (Especially when we get into namespaces, linking, inclusion
and validation, and PSVIs)

Has anyone ever documented what these separate layers are?
Or possibly identified in which 'layer' particular XML
requirements/constraint
lie?

Is it possible to write an efficient layered parser in this way?

Do the logical divisions get blurred once optimisation starts?

Not having ever written an XML parser I'm not an expert, but it
seems like there's either some common assumptions which might
be worth clarifying, or perhaps a slowly developing consensus about
the best way to build modular XML frameworks.

(Simons recent thread on 'filtering noise' seems like another facet
to this.)

If its the latter it appears (to me at least) as if its being driven
by an increasing distance from the SGML heritage, and the need to
deal with, and rationalise, the number of additional specifications being
built
upon the XML foundations.

Any comments?

L.

--
Leigh Dodds, Systems Architect       | "Pluralitas non est ponenda
http://weblogs.userland.com/eclectic |    sine necessitate"
http://www.xml.com/pub/xmldeviant    |     -- William of Ockham