PITarget uniqueness

james anderson James.Anderson at mecomnet.de
Sun Apr 11 17:39:46 BST 1999

i've always had a nagging feeling of uncertainty in the past when i've read
the statement which is cited below. when i asked, way back, for example, why
one was not allowed to qualify notation names and pi targets, the answer was,
that it was expected that they would be bound to URI's. this may well be true,
but it doesn't matter. the two mechanisms are behave differently.

namespaces wrt element and attribute names are part of a mechanism of the form

   prefix X local-part  -> prefix X URI -> URI X local-Part = universal-name

the PI / notation mechanism, on the other hand, is of the form

   local-part -> local-part X URI -> URI

these are different things. they both concern URI's but behave differently wrt
name collisions and the extent to which late binding can be used to avoid such.

if, for example, two documents are to be combined within which encoded element
identifiers and encoded PI targets conflict, late bound prefixes can "fix" the
former, but you can't do anything about the latter.

one may object, that the notations are "registered", and as such ambiguous,
but that's not the problem. it's the pi targets themselves. if you can't map
them late, you're effectively registering them and the notation - in
particular the uri in the notation - is redundant, and thus superfluous.

one may object, that it's actually not a pi-target == local-part, but a
pi-target == prefix equivalence which is is at work here, and dynamicaly
generated pi-targets solve the problem, but that contradicts the claims made
wrt element/attribute identifiers and the need for dynamic prefix/URI bindings.

John Cowan wrote:
> James Tauber wrote:
> > PI targets can be associated with a URI using the NOTATION mechanism. This
> > is so much like the namespace mechanism that I'd really like it if the two
> > were merged and the PI target made arbitrary.

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