# Re: Grainularity of URN

John Curran (jcurran@nic.near.net)
Thu, 20 May 1993 21:16:14 -0400

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    Message-Id: <9305210116.AA02770@mocha.bunyip.com>

    To: Putz.PARC@xerox.com

    Subject: Re: Grainularity of URN

    In-Reply-To: Your message of Thu, 20 May 1993 14:23:25 -0700.

                 <93May20.142345pdt.2445@spoggles.parc.xerox.com>

    Date: Thu, 20 May 1993 21:16:14 -0400

    From: John Curran <jcurran@nic.near.net>

--------
] From: Putz.PARC@xerox.com
] Subject: Re: Grainularity of URN
] Date: Thu, 20 May 1993 14:23:25 PDT
]
] 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.
]
] Which brings up the question of whether a given URN should be allowed
] to map to multiple URLs for different representations of a document (e.g.
] FrameMaker, PostScript, TIFF, ASCII).

It is likely that we will want to have URN's that refer to portion of
the resources in a logical manner. For example, a resource may be known
as <URN:jcurran.near.net::silly-idea:::> and yet a portion will be known
as <URN:jcurran.near.net::silly-idea/abstract:::>.

It is also likely that we will want to have _URL's_ which reference a
fragment of a particular instantiation of a resource. As an example, if
the URL for the first URN above was "ftp://ftp.near.net/docs/silly-idea.txt"
the second URN could be "ftp://ftp.near.net/docs/silly-idea.txt:231-1342".
The important point is that we should keep URN fragments refer to logical
elements (paragraphs, images, audio segments, etc...) and have URL fragments
used for physical elements (bytes, pages, second offsets, etc...)

/John

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