# Re: Unresolvable URNs

Tim Berners-Lee (timbl@ptpc00.cern.ch)
Mon, 21 Feb 94 15:53:44 +0100

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    Date: Mon, 21 Feb 94 15:53:44 +0100

    From: Tim Berners-Lee <timbl@ptpc00.cern.ch>

    Message-Id: <9402211453.AA01922@ptpc00.cern.ch>

    To: David Robison <robison@nwnet.net>

    Subject: Re: Unresolvable URNs

David Robison <robison@nwnet.net> says:
> A correction is in order here: ISBNs are not opaque. They are made up of

> 4 discrete sections: the first represents language/country; the second is

> the publisher number; the third is the book number (simply and ordinal);

> the last digit is a check digit.

What do you mean my "opaque"? They are used by most people without the
knowledge that you have. They are pretty opaque to me :-)
When you order a book by ISBN, does the bookshop look up
the list of publisher prefixes? Is there a resolution algorithm
well defined?

An interesting point is that you can't determine where the boundaries
lie between the fields. So the ISBN authorities can cook up
flexible (classless a la CIDR) allocation spaces without worrying the man
in the street. But as you say, they dropped it when it came to
the fixed length. (They just chose 10**9 instead of 2**32 :-)
I guess variable-length bar code technology wasn't there at the time.

Tim BL

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- Maybe in reply to: Jim McBeath: "Unresolvable URNs"
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- Reply: David Robison: "Re: Unresolvable URNs --> ISBNs (discussion, not resolution)"