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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Semantic equivalence of xml documents
At 13:46 +0200 2005-09-26, Yves Langisch wrote:
>Michael,
>
>I mean for example that
>
><company>
> <person>Jim</person>
> <person>John</person>
></company>
>
>is equivalent to
>
><company>
> <person>John</person>
> <person>Jim</person>
></company>
>
>Yves
Yves,
Whether these two are "equivalent" depends on your situation. They
are of course not precisely "equal", but for your particular schema
and your particular purposes the count as equal. That's fine, but
perhaps in someone's schema the first <person> in each <company> is
the president, so the two cases would have very different semantics.
Once you define *exactly* what you mean by equivalence, you will be
able to find tools to help check it. You will need to decide very
specifically what equivalence means. You may need a rule for each
element. It is probably true that only some of your elements can be
re-ordered this way, not all of them. You will have to tell the
computer exactly which ones.
If the only unusual case is reordering, then one way to do your tests
would be to write XSLT to sort the elements in question (like
<person> here). Then, after the sorting, you could just do a regular
comparison.
Depending on your situation, you may have harder problems. For example, is
<p style='first-indent:1in'>
equivalent to
<p style='first-indent:72pt;'>
I don't know of any tools that will help with that sort of thing. As
Michael pointed out, if you also want to really check the "meaning"
of the sentences within the document that is a very hard problem.
Usually, when we talk about two XML documents being "equivalent," we
mean syntax, not semantics. This is because the semantics of XML are
not defined. So there are well-known methods to decide about syntax
cases like
<p type='foo'>
versus
<p type = "foo" >
But for truly semantic issues like what you seem to need, the problem
is much harder.
Once you define exactly what you mean by equivalence and get it
written down very precisely, you may be able to check a lot of it
with XSLT followed by syntax comparisons, or other methods. But until
one knows precisely what is required, it's hard to advise about tools.
If you want assistance in figuring out just what equivalence means
for your project, that may be a large question, and may be an
appropriate area to seek help from any of the excellent consultants
available on the list.
Steve DeRose
--
Luthien Consulting: Real solutions to hard information management problems
Specializing in information design, XML, schemas, XSLT, and
project design/review/repair
Steven J. DeRose, Ph.D., sderose@a...
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