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Link-3: Sets, Singletons, and Determinism

From: Tim Bray <tbray@textuality.com>
Date: Sun, 18 May 1997 11:38:00 -0700
Message-Id: <>
To: w3c-sgml-wg@w3.org
Although XML-link currently doesn't address this at all, the spec probably 
follows the TEI principal of determinism; that is to say, you always get 
exactly one location as the result of an xpointer (or in the case of spans, 

If we are going to allow spans, and thus an xpointer to return N
locations, where N>1, should we consider saying that all xpointers
return sets of objects, and sometimes the size of the set is 1?  This
would open up a whole bunch of interesting apps.

On the other hand, it would make xpointers smell even more like queries
and less like addresses, which makes me at least nervous.  We also
have to be careful if we are going to (see a later message) allow
sub-element addressing; then we'd have to say that either that is
a set of one pseudo-element, or that xpointers can return either
sets of elements or spans of characters.  Tricky either way... but
returning sets of elements is a seductive idea.

Cheers, Tim Bray
tbray@textuality.com http://www.textuality.com/ +1-604-708-9592
Received on Sunday, 18 May 1997 05:38:20 UTC

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