namespaces and XML validation
James.Anderson at mecomnet.de
Mon Aug 10 01:23:58 BST 1998
pi-declared v/s attribute-declared namespaces do not make any difference to validation.
the present wd leaves some ambiguities which affect namespace identification,
but that leads to problems with all sorts of things, not just validation.
the algorithm sketched out in mr bray's note is the 'string-processing'
equivalent of the 'symbol-processing' approach which i have been advocating
since the appearance of the previous draft. the 're-prefixed' names are the
equivalent of the pointer to an interned symbol. this is sufficient to
validate against dtd's from arbitrary namespaces.
the advantage of a symbol based approach is that it accomplishes the 'rewrite'
in one pass as in integral part of the parse. if the unambiguous serial form
is required for whatever reason, it can be created by simply reserializing the document.
at its most basic, the symbol-based approach would require that the name type
suggested by mr megginson be modified to comprise a package and a local name
rather than an uri and a local name; to place the uri in the package; and to
use the package as the map between the local name and the universal name.
which name is then bound into all elements, attributes, element declarations,
etc., where one would now use a string.
an advantage of interning by means of a package, rather than a global set of
universal names is that it is easier to place a symbol in more than one
package. this is often useful.
according to the wd. prefixes need be bound dynamically to packages only in
the process of parsing elements (modulo the issues of lexical scope for prefix
bindings for dom side-effects)
in order to satisfy the assumption re "knowing where each name in the dtd
comes from", one also needs to bind dynamically (at least) at entity
boundaries (the document proper, the external subset, external entities). note
that, if this is not supported, then validation is not the only thing which
suffers. validation suffers as a side effect of not being able to guarantee
the identity of a name, which means, strictly speaking that no form of
declaration-based processing is possible.
i've dismissed elevating prefixes to universal status, since it's easy to come
up with cases where that method fails. why did the wg dismiss using additional
pseudo attributes on the xml declaration and on entity declarations to bind
prefixes within those entities? in the present spec, where no namespace
bindings extend over the dtd, there's no reason to read it, since it can't be
guaranteed to have an unambiguous interpretation.
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