ID and tag value uniqueness, how?
M.H.Kay at eng.icl.co.uk
Fri Oct 30 10:19:46 GMT 1998
>> I want each action item to have a *unique* number that can
>> automatically be validated during the parser process.
>The other thing to consider is whether the parser will even enforce
uniqueness. This is a validity constraint, >and lots of parsers don't
enforce validity. So your choice is either to always use a known,
validating parser or >write the enforcement code yourself.
I've hit this problem myself. One thing I would like in SAX 2.0 is the
ability to tell the parser that I expect it to do validation.
In practice because I couldn't rely on the parser to check uniqueness, and
because I was doing so much other "semantic" validation anyway (e.g. valid
dates, etc), I decided that I might as well do the uniqueness check myself.
I needed to build a dictionary of identifiers anyway to resolve IDREF
references: a validating parser will tell you whether an IDREF is valid, but
it won't necessarily tell you what it points to!
PS. What confused me in the original question, however, was:
>Is it possible to use XML and/or DTD and/or the parser to generate unique
>ID's - I would think that would solve my (part of the) problem.
Generating ID's during parsing is of course is a different question from
validating IDs stored in the original XML.
One easy way to get numbers generated during parsing is to use SAXON - there
is an example in the automatic numbering of verses in the New Testament
rendition I published recently on this list.
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