System URIs

[Rob Lugt <roblugt@elcel.com>]

I have two questions regarding the treatment of System URIs:

1)  The draft specification (17 May) Section 5.x has several references to
the *normalized* value of the systemId attribute, but the specification does
not contain details of the normalization algorithm.  I presume this involves
the escaping of illegal URI characters as described in XML 1.0, 4.2.2
External Entities [1].

2)  The specification makes no mention of how relative system URIs will be
dealt with.  I take it, therefore, that they will be dealt with in the
literal way, i.e. they must match lexicographically with the entry in the
system catalog.  In practice this probably means that a local copy of an XML
entity (a DTD say) will need to also contain all the relatively-referenced
entities.  I think that:
a)  It might be helpful if the specification points out that no attempt
should be made to normalize relative system URIs into absolute URIs
b)  The committee should consider disallowing relative URIs in the systemId
and systemIdStartString parameters.

Point (a) would be useful to aid understanding, point (b) would be useful to
improve the performance of applications using the XML Catalog.  Performance
could be improved because the EntityResolver would be able to skip the
lookup of relative URIs.

The potential performance improvement could be significant if the catalog
contains nextCatalog entries because, for relative URIs, it is likely that
all catalog entry files will be searched without success.

Regards
Rob Lugt
ElCel Technology

[1] http://www.w3.org/TR/REC-xml#sec-external-ent


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