Deterministic behavior in processors

[Tim Bray]

At 02:00 PM 8/4/98 -0400, Dean Roddey wrote:
>Hmmm. Ok I'm going to play the "Very Cynical Devil's Advocate" here and ask the
>obvious question of "Is a spec that allows 2^7'th conforming variations really
>a spec?" 
...
>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 
behavior of a NVP is non-deterministic has bothered not a few
people in the XML process; there's even an appendix in the spec that
talks about this.  

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

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.

One extrapolation from this argument is that external entities are
bogus and shouldn't have made it into XML.  I believe this, but only
about 48% of the time. 

Another extrapolation is that we should decree that NVP's *never*
read external entities.  But in the authoring situation, having 
an NVP be potentially able to read something like

<book>
 &chap1;
 &chap2;
</book>

is handy enough that it seems senseless to rule it out just because
it opens the door to really stupid behavior, viz. sending external
entities over the wire without specifying a validating processor.
-Tim

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