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Re: Deterministic behavior in processors

• From: Peter Murray-Rust <peter@u...>
• To: <xml-dev@i...>
• Date: Wed, 05 Aug 1998 09:46:10

At 23:16 04/08/98 -0700, Tim Bray wrote:
>At 02:00 PM 8/4/98 -0400, Dean Roddey wrote:
[...]
>>It would serve
>>everyone's best interests (IMHO) to have a very tight specification in which
>>there are very few optional reactions to the same circumstances.
>
>Basically I think this concern is reasonable, and the fact that the 

So do I. I have always worried about what the parser actually does and emits.

>As a registered minimalist, it never really bothered me, because I
>have always thought that external entities were pretty bogus outside
>the authoring arena anyhow, and anybody who sends anything across the
>wire had better either:
>
>(a) guarantee no external entities, or
>(b) potentially have external entities AND specify use of a validating
>    processor

This really worries me and puts me in the rocks-in-head category. I have
blithely assumed that external entities were a good thing. They represent a
way of re-using and normalising information. I've even been telling people
they are a good thing.

>
>In both of these scenarios the behavior is completely deterministic.
>
>I think that anyone who sends XML across the wire and uses external
>entities and does not specify a validating processor has rocks in their
>head and deserves what they get.

Gulp. That's me. I have been reading the spec on and off for two years and
I have clearly failed to understand this. I am suffering from SAXocephaly.
I use the following construct frequently:

<!DOCTYPE FOO [
<!ENTITY a SYSTEM "a.xml">
<!ENTITY b SYSTEM "b.xml">
]>
<FOO>
&a;
&b;
</FOO>

I have briefly re-read the spec and it's not immediately clear to me where
it says that a NVP is allowed to neglect a and b if it's feeling lazy. (It
does say that if these are in an external subset they can be neglected, I
think.)

I would hesitate to criticise the spec but if the above document does not
mean what I think it should mean (or worse, depends on what software I use)
then I have serious problems. I *can't* use a validating parser because
it's impossible to construct a DTD for the complex information in a.xml and
b.xml (uses at least 4 namespaces). I don't want a parser which bombs on
the first 'invalidity' fatal error - i.e. doesn't have a DTD.

	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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