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should all XML parsers reject non-deterministic content models?
- From: "TAKAHASHI Hideo(BSD-13G)" <email@example.com>
- To: firstname.lastname@example.org
- Date: Sun, 14 Jan 2001 16:42:55 +0900
I understand that the XML 1.0 spec prohibits non-deterministic (or,
ambiguous) content models (for compatibility, to be precise).
Are all xml 1.0 compliant xml processing software required to reject
DTDs with such content models?
Ambiguous content models doesn't cause any problems when you construct a
DFA via an NFA. I have heard that there is a way to construct DFAs
directly from regexps without making an NFA, but that method can't
handle non-deterministic regular expressions. If you choose that method
to construct your DFA, you will surely benefit from the rule in XML 1.0
. But if you choose not, detecting non-deterministic content models
become an extra job.
I can see that parsers that allow non-deterministic content models may
be harmful to the user. The user won't notice that his DTD may be
rejected by other parsers.
So there seems to be good reason for the XML 1.0 spec to prohibit
parsers that accept non-deterministic content models. In that case the
spec not only gives chance for a particular DFA constructing algorithm
to be used, but effectively recommends the usage of the algorithm.