Next message: Geoffrey M. Clemm: "Re: Stable URLs"
Date: Mon, 10 Apr 2000 23:24:32 -0400 (EDT)
Message-Id: <200004110324.XAA10259@tantalum.atria.com>
From: "Geoffrey M. Clemm" <geoffrey.clemm@rational.com>
To: ietf-dav-versioning@w3.org
Subject: Re: Questions on activities
From: jamsden@us.ibm.com
<geoff> The reason CM systems restrict the names of versioning
metadata is because those restrictions are essential for an
implementation that scales. In particular, you can't efficiently
cache information that is out of your control (i.e. in a namespace
you don't control). So versioning metadata names will need to be
restricted in order to provide CM functionality for the number of
resources found on today's web sites. </geoff>
<jra> Perhaps I'm missing something, but I don't see this. I agree
that CM systems need to make all kinds of restrictions in order to
manage the integrity of their repositories, and provide efficient
implementations through predictable caching. But I don't see what
this has to do with a WebDAV server that interfaces to these CM
systems. I think the server mappings to the CM system allow the CM
system to maintain its restrictions while the additional
flexibility is implemented only in the WebDAV server.
The majority of web servers (such as Apache and IIS) only handle a few
top level name mappings, and hand the rest of the processing off to
the underlying repository. So it is reasonable to associate some
collection with a class of metadata, and map the URL of that
collection to the appropriate underlying repository, but this does not
allow you to make arbitrary associations between URL's and different
kinds of metadata potentially from different repositories.
So for example, the CM system can do all the caching it wants, and
restrict versioning metadata as necessary to make it efficient.
Its up to the WebDAV server implementation on that CM system to
manage its bindings to the cached and restriced resources,
including any additional caching and restrictions the WebDAV server
may wish to impose on its behalf. Its using WebDAV as an
associative object between the many-to-many association betwen
clients and CM systems that enables this flexibility.
While we are waiting for such WebDAV servers to be written, I'd like
to make it possible to have implementations that are significantly
simpler, and assume all but the top level name mappings are being
maintained by the underlying repository.
So I don't
think these CM restrictions are invalid, I just don't think the
necessarily need to be exposed in the WebDAV protocol. Make sense?
</jra>
Another reason to allow repositories to do most of the name mapping
is that many users want to use several protocols to access a repository,
and don't want to have to remember (and maintain) several namespaces
to access data in the same repository.
Cheers,
Geoff