Re: Draft Combined Requirements Document

At 12:20 AM 2/11/97, Fabio Vitali wrote:
>Dear all,
>> A way to determine whether a given URL points to a version
>>of a versioned resource.
>>***Judy - Are we requiring that you be able to tell this just by
>>examining the URL?
>Ehm, yes. The URL does not contain enough information to be able to
>determine the position of the version in the version tree, but enough to be
>able to tell a versioned resource from an unversioned one. At least this is
>what we came in July, when we discussed about these things,I think.

Well, no, actually... All the people who just do versioning thought that
some URI-based scheme was the most sensible. The W3C position, strongly
articulated by Dan Connolly, was that any interpretation of URLs was not

Without arguing the merits of that approach (I disagree that is it a useful
restriction in this case), we said "a method" in order to allow the group
to decide whether "URL-hacking" or new HTTP methods were the best
implementation. So the function is required. The obvious implementation in
terms of URLs can come up for discussion again. The early archives of the
versioning discussion have a great deal of discussion of this point.

>> A way to distinguish, given a URL of a version, the part of
>>the URL that identifies the version from the part that identifies the
>>versioned resource.
>>***Judy - Do we really have to (want to) require that you be able to
>>find out the URL of the versioned resource by examining the URL of the
>>version?  Is the requirement really just that there be some way to find
>>out, for any version, the URL of its versioned resource?
>Well, the idea was to have the URL of a version to be "something more" than
>the URL of the whole resource, and that this "something more", although
>opaque to the client, could be easily separated from the rest of the URL,
>so that it was possible to find out the whole resource, given one version
>of it.]

As above, "URL-hacking" was a controversial approach that some were not
willing to accept. The functionality is crucial, but if URLs cannot be
interpreted new HTTP methods are needed, and a round-trip is required for
certain obvious operations.

>I propose that we start considering the issue of a MIME type to contain
>partial update data, and that we start developing a common format. I also
>propose VTML as a basis for it. I will post the latest spec of VTML if
>there is interest in this.

I will add that VTML also contains facilities to send multiple versions of
a document in a single reasonably organized package. This is essentially a
simplification/generalization for general stream of the kind of information
kept in a version repository.

   -- David

David Durand              dgd@cs.bu.edu  \  david@dynamicDiagrams.com
Boston University Computer Science        \  Sr. Analyst
http://www.cs.bu.edu/students/grads/dgd/   \  Dynamic Diagrams
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