# Re: Grainularity of URN

David G. Durand (dgd@cs.bu.edu)
Fri, 21 May 1993 11:17:53 -0800

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    Message-Id: <9305211515.AA10250@cs.bu.edu>

    Date: Fri, 21 May 1993 11:17:53 -0800

    To: uri@bunyip.com

    From: David G. Durand <dgd@cs.bu.edu>

    Subject: Re: Grainularity of URN

>Dirk Herr-Hoyman wrote:
>> But, it's not clear to me how an anchor fits into URNs?
>
>Well, a URN is supposed to be a name that can be turned into a URL when
>necessary (via some kind of name lookup service), and if you believe (I
>don't) that named anchors in URLs are a sufficient way to refer to portions of
>a document, then I suppose the trick is just getting another URN assigned to
>the portion of the document you are interested in.
>
>But it is not really that simple. Even with URLs to HTML documents, you
>cannot refer to a portion of document unless the author has put in a named
>anchor where you want it. And there is no way to refer to a segment or
>range of a document, rather than a single point. Using character positions
>is not robust across end-of-line conversions for ASCII files, much less
>across versions of a document or conversions into different formats.
>some stuff deleted
>Steve Putz
>Xerox Palo Alto Research Center

I've been trying to follow this discussion, but the pressures of other
work (and the current volume of discussion) are making it difficult. One of
my research interests is collaborative editing/and revision control of
strcutured documents. The solutions that come out of this sort of problem
(at least the ones that I favor) generally need large numbers of unique
identifiers, since in general each operation performed by a user needs a
unique ID (one can identify data by the operation that created it)

It also seems pretty obvious that some kind of universal adressing is
needed for portions of documents, without requiring those documents to be
modified. This is certainly going to be needed for interactive and
collaborative hypertexts. One easy (though not super-flexible) way to get
this is to require version numbers, and have versions specify a particular
encoding scheme and fixed byte sequence -- ie. each docuemnt would contain
a specification of its encoding for newlines and the like -- then byte
offsets can be used.

I've still to read all the relevant documents, so I'm not commenting on
the proposals, but trying to give a perspective on a different view of the
problems you mention, and (perhaps) unusual applications of universal names
(ie. naming small portions of documents). I also think that a URN must name
an immutable object in order for internal anchors to work, and that implies
that some hooks must be left for version control for those applications
that will support it.

-- David Durand
Boston University Computer Science

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