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Re: Translation in the Tower of Babble

From: Eric Sedlar <esedlar@us.oracle.com>
Date: Mon, 03 Jan 2000 16:08:31 -0800
Message-ID: <387139FF.100634F4@us.oracle.com>
To: Yaron Goland <yarong@Exchange.Microsoft.com>
CC: w3c-dist-auth@w3.org, "'gclemm@atria.com'" <gclemm@atria.com>

The problem with discussing abstractions like this without concrete examples is
like trying to write legislation without loopholes--you don't really know if
it's well written until you see its effects.

My guess is that the direction you are heading in is defining a resource as the
base class of all WebDAV objects capable of responding to an HTTP request.
This is a good abstraction.  It follows from this that an HTTP method like LOCK
should not apply to a URL that does not identify a resource, since there is no
resource to respond to the request, which would outlaw the lock-null approach.

It might be useful to give more of an "agenda" for where this thread is going
(even without filling in the details), so people can better place your
discussion in context of the world of WebDAV problems.

In general, however, I think that any solution to the locking problems
discussed recently has to fit in some general model like the one I anticipate
that Yaron will propose.  However, I prefer a complete model to be laid out
before me before I comment on particular precepts of the model.

For example, following this level of abstraction, we should define a resource
better.  I would say that a resource has a set of properties, which can be
represented via an XML document.  Some of these properties are
"live" properties, which are read-only and are set as a side effect of other
methods ( for example a modification date).  Attempts to set the value of a
live property directly via generic property mutator method(s) (e.g. PROPPATCH,
PUT, etc.) should always be ignored.  A collection is a subclass of resource
that has a live property containing a list of tuples including at least a name
(and possibly with other values such as a resource ID associated with that
name).  A BIND request is treated as a method that modifies the values of the
collection's name tuple list.

This should all be worked into the versioning model document
(http://www.ics.uci.edu/pub/ietf/webdav/versioning/model990209/), which while
defining some of the functional methods available on a resource, doesn't define
the properties on a resource as well as a number of the other assumptions along
the lines Yaron proposes.


Yaron Goland wrote:

> I believe that there are too many different unstated assumptions held by
> members of this group for this group to be ready to deal with specific
> locking proposals. The fact that Geoff, Eric and RFC 2518 can come out with
> such different proposals helps to illustrate the issue. Rather than
> attempting to achieve consensus in one fell swoop by having everyone read
> and critique full proposals I would suggest that we start from a simpler
> basis. Let us first see if we can establish agreement on some very basic
> precepts. I will start with just one precept and see if we can get agreement
> on just that.
> Precept #1 - HTTP clients send HTTP request messages to resources that
> respond with HTTP response messages.
> Corollary #1.1 - All HTTP proposals can only be written in terms of how a
> resource processes a HTTP request from a HTTP client and generates a HTTP
> response as a result.
> Corollary #1.2 - HTTP requests do not necessarily have to be handled by HTTP
> resources. For example, it is possible to send a HTTP request with a FTP
> request-URI. Some HTTP proxies are set up to act as gateways that can handle
> translating the HTTP request into a FTP request and then translate the FTP
> response into a HTTP response. That is why precept #1 states "...to
> resources..." rather than specifying a HTTP resource.
> Corollary #1.3 - Since HTTP request messages can only be handled by
> resources which respond with HTTP response messages then even error messages
> such as "Not Found" must have been generated by a resource.
> Let's see if we can just get agreement on this single precept and its
> corollaries.
>         Merci,
>                         Yaron
Received on Monday, 3 January 2000 19:01:22 UTC

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