RE: Clarification of URI vs. resource

I believe the sentence that is giving so much pain is from section 5.2 of
v9:


   Any given internal member MUST only belong to the collection once,
   i.e., it is illegal to have multiple instances of the same URI in a
   collection.


The intention is to say that you can't have the same URI be listed twice as
a member of a collection. However I can see how someone would read our
reference to internal member (which is defined in terms of URIs not
resources) as meaning a resource.

How about:

	The same URI MUST NOT appear more than once as a member of a
collection.

This would replace the previous sentence in total.

		Yaron

-----Original Message-----
From: Jim Whitehead [mailto:ejw@ics.uci.edu]
Sent: Friday, November 13, 1998 9:30 AM
To: Larry Masinter
Cc: w3c-dist-auth@w3.org
Subject: RE: Clarification of URI vs. resource 


Larry Masinter writes:
> Urk! That wasn't what I was complaining about. The requirement I
> don't understand is the requirement that a resource not appear
> twice in a collection. I don't understand the reason for the requirement.
> If I understood the reason for the requirement, then I might know
> why it should be OK for the same 'resource' to appear in a collection
> twice if that resource is named with different URLs.

The requirement is intended to be: the same *URL* cannot appear more than
once in the same collection.  Multiple instances of the same *resource* are
allowed.

One rationale for this requirement is to avoid having to have "instance"
identifiers for each URL in a collection, and to avoid handling ordering
issues in the base specification.

The other rationale for this requirement is that having multiple instances
of the same URL in a collection just didn't make sense.  For example,
assuming multiple instances of the same URL are allowed in a collection, if
there is a collection resource R, with URL
http://www.example.com/collection/, and it has members:

./hello.html
./logo.gif
./hello.html

That is, when accessed via URL http://www.example.com/collection/ the
absolute form of the URLs of these members is:

http://www.example.com/collection/hello.html
http://www.example.com/collection/logo.gif
http://www.example.com/collection/hello.html

What does it mean to have ./hello.html twice?  How can one of these
duplicates be created?  If one instance is deleted, the others must go away
as well (or leave a dangling member of collection).  This issue of having
multiple instances of the same URL in a collection was discussed in the
advanced collections specification as well, and the decision was made there
too not to have multiple instances of the same URL in a collection.

- Jim

Received on Friday, 13 November 1998 16:12:08 UTC