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RE: Collections, Resourcetype and Hierarchy in WebDAV

From: Larry Masinter <masinter@parc.xerox.com>
Date: Sun, 27 Dec 1998 15:55:26 PST
To: "Yaron Goland" <yarong@microsoft.com>, "WEBDAV WG" <w3c-dist-auth@w3.org>
Message-ID: <000001be31f4$60889e60$d111020d@copper.parc.xerox.com>
> 1 Why Did WebDAV Decide that the HTTP URL Namespace is a Hierarchy?

I don't find the answer to this question very satisfying.
It sounds like "the working group decided to do this
because the working group decided to do this".

> A typical HTTP URL looks like http://server.com/name1/name2/name3. The
> HTTP/1.1 specification never defined what the "/" really meant.
> Did the "/"s have any meaning or were they just decoration to
> help people remember where they put their resources? This was
> one of the very first problems the WebDAV Working Group (WG) had to face.

It's not clear why this problem was 'faced' by the working group.
I mean, does the "1" in "name1" have any meaning, or is it just
decoration? Why is this a problem?

> Most of the WG had the very definite idea that WebDAV should
> provide at least file system level functionality.

The problem is that the notion of 'file system level functionality'
is pretty fuzzy, and 'at least' is even fuzzier (which file system?).
Even though most of the WG might agree on a general principle, it
isn't clear that this is a good decision process for deciding on
a particular feature. In particular, it might be desirable to have
a client be able to determine at least one collection that contains
a given resource, if one is known, but it's not at at clear that
the requirement that there be a single canonical parent that contains
any resource corresponds to 'at least file system level functionality'.
In fact, we have lots of counterexamples of file systems for which
this requirement doesn't match at all (just to pick one example,
unix file systems which allow 'hard links').


> document management types who didn't really use file systems, they
> understood that file systems were the single most common form of
> storage on the planet. Matching file system functionality meant providing
at
> least the possibility of supporting a hierarchical namespace.

But WebDAV doesn't "match" file system functionality in this
regard. Rather, WebDAV chose to emulate a very restricted
model of file system, and require this model for all of
the WebDAV servers.

> So the WG decided that the "/"s could represent a hierarchical
> namespace and that it was WebDAV's job to provide the tools to
> create and maintain that hierarchy if the client/server choose
> to make it hierarchical.

It's exactly this problem, that the client and server mutually
have to agree on the semantics, that makes this a serious problem
for WebDAV interoperability. Clients that are written to assume
DOS-like file systems will not interoperate with other storage systems
that don't have such restrictive semantics.

Larry
Received on Sunday, 27 December 1998 18:56:03 GMT

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