Overloaded URIs (was Re: XLink: behavior must go!)

Andrew Layman andrewl at microsoft.com
Fri May 21 19:55:37 BST 1999

Speaking about namespaces, Nikita Ogivetsky wrote "And in some cases like
with xsl, xlink, etc. the alias itself becomes unique ( even though one can
use the word "reserved"). And the URI becomes a version number."

What do you mean by this?  Do you mean that sometimes a namespace prefix is
an alias to a URI, where the particular prefix is immaterial and it is the
URI that identifies the namespace, while at other times the namespace is
identified by the specifc prefix employed?

If this is your meaning, I recommend that you study sections 1, 2 and 3 of
the namespaces specification, http://www.w3.org/TR/REC-xml-names/, paying
particular attention to the exact definitions of the various terms and to
the sentance reading "Note that the prefix functions only as a placeholder
for a namespace name. Applications should use the namespace name, not the
prefix, in constructing names whose scope extends beyond the containing

Another useful document to read is Tim Berners-Lee's "Web Architecture from
50,000 feet" at http://www.w3.org/DesignIssues/Architecture.html,
particularly the passage "Guidelines for new Web developments are that they
should respect the generic definition and syntax of URIs, not introduce new
URI schemes without due cause, not introduce any different scheme which puts
itself forward as to be universal as a superset of URIs which would
effectively require information apart from a URI to be used as a reference.
Also, in new developments, all significant objects with any form of
persistent identity should be "first class objects" for which a URI exists.
New systems should use URIs where a reference exists, without making
constraint on the scheme (old or new) which is chosen."

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