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Possible schema issues relating to cycles of include and redefine

From: <noah_mendelsohn@us.ibm.com>
Date: Wed, 28 Jul 2004 22:25:41 -0400
To: www-xml-schema-comments@w3.org
Message-ID: <OFF72B64BB.9EBF2FAE-ON85256EDF.007CBD37@lotus.com>

We are careful in the recommendation to allow for repeated inclusion of the
same file (see note at the end of [1]).  We are not particularly clear, I
think, on whether cycles of includes are allowed.  My own belief is that
they should be, and that a clarification should be issued as an erratum (at
a convenient time) to warn implementors that guarding against loops is
required.  Or, we could rule out cycles, perhaps warning users that some
processors will indeed loop forever.  Either way, I suggest a
clarification.  Maybe or maybe not we need to bring into the discussion the
possible impact of chains of includes, imports for which schemaLocation is
honored, etc. possibly across namespaces, but resulting in cycles.

Similarly, I think the recommendation would benefit from clarification of
the rules relating to cycles of redefines.  In most cases, these will
produce invalid components due to violations of rules on restriction or
extension, I think, but there may be other cases that are not clearly ruled
out.  I think cycles of redefinition should be prohibited.


[1] http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#compound-schema

Noah Mendelsohn
IBM Corporation
One Rogers Street
Cambridge, MA 02142
Received on Wednesday, 28 July 2004 23:31:36 UTC

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