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RE: Status code for creating lock-null resource

From: Jim Whitehead <ejw@cse.ucsc.edu>
Date: Fri, 15 Jun 2001 11:51:13 -0700
To: "WebDAV WG" <w3c-dist-auth@w3.org>
> > 2) A null resource MUST NOT appear as a member of its parent
> > collection (RFC2518 sec 3).
> That's interesting, because Section 7.4 (which I was reading) states that
> it MUST appear as a member of its parent collection.<g>
> By copy to JimW.  Please add this to the RFC2518 issues list.

Actually, the specification is correct, though it takes a careful read to
see that.

There is a difference between a "null" resource, and a "lock null" resource.
The definition of a "null" resource, as given in Section 3, is correct. Lock
null resources are defined in Section 7.4. A null resource does not belong
to its parent collection, and does not respond to UNLOCK. Perhaps a better
way to express this concept is that what we termed a "null resource" is
really an "unmapped URL". That is, the URL is not mapped to a resource. This
avoids the philosophical question of "is a null resource a resource"? By
calling it an unmapped URL, a "null resource" is clearly not a resource.

A lock-null resource is a null resource that has been locked.  A lock null
resource has diferent properties that a null resource. Specifically, it has
at least the lock discovery properties, and it is a member of its parent's

> > 4) Lock null resources (LNRs) are there to reserve name (RFC2518
> > sec 7.4). They are there so a client can reserve the name *before
> > they create the resource* (store the "entity"). Admittedly, a
> > server may use a file to represent the LNR, but thats an
> > implementation detail. Since the name is reserved, it avoids
> > potential conflict when the entity is actually stored e.g. with
> > a PUT.
> I couldn't find the bit about "before they create the resource".
> The use of a file is a red herring, I have never suggested that any DAV
> server has to use files at all, in fact the opposite, I've always objected
> to such statements.
> If a lock null resource is not a resource, then what is it?

Since a lock null resource has state, I would claim it is a resource. By the
act of a client taking out a lock, they have likely made a mapping of a URL
to a conceptual resource, and are int he process of fleshing out the
computer representation of the conceptual resource.

- Jim
Received on Friday, 15 June 2001 14:53:28 UTC

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