Subject: Re: [urn] several different proposals for URN syntax to include fragments and queries

From: Juha Hakala <[email-masked]>
Date: Thu, 11 Jul 2013 09:08:20 +0300

Hello,

On 22.6.2013 17:49, Keith Moore wrote:
> On 06/22/2013 09:16 AM, Barry Leiba wrote:
>
> None of the examples you cited above require use of a query string 
> within the URN.   A URN can be associated with a query without having 
> to contain a query string.   The only reason for a URN to contain a 
> query string is if you want to be able to substitute one query string 
> for another, or to expose the relationship between the query and the 
> base resource (i.e. the query engine) for some other reason.
>
>> And yet I can see value, for research and reference purposes, to have
>> "a URN" that names "all books written by Barack Obama" (as opposed to
>> "all books *about* Barack Obama", which, to me, would clearly be a
>> transient query).
>
> No, "all books about Barack Obama" would not clearly be a transient 
> query.

In OCLC's Worldcat database it is easy to search resources created by Obama

http://www.worldcat.org/search?q=au%3Aobama%2C+barack&qt=advanced&dblist=638

or resources about him:

http://www.worldcat.org/search?q=kw%3Aobama%2C+barack&qt=advanced&dblist=638

The results sets overlap, but in the former set there are about 1000 
hits, the latter has almost 12.000.

There are no plans to assign URNs or other truly persistent identifiers 
to database searches such as the ones above, not least because the 
result sets will be constantly growing. The two URLs above are not 
likely to be persistent in the national library scale of things, and 
they don't even need to be that.

Hypothetical examples of meaningful ways of using URN + query in this 
particular context include the following:

1. Using URN:ISTC, find all versions (printed and audio book, 
translations to other languages, etc) of one of Obama's books, Dreams 
from my father.

2. Using URN:ISBN, retrieve PDF edition of Dreams of my father or find 
out if there are other digital editions of it

3. Using URN:ISBN, find out if there is a copy of the PDF edition out 
there that I can access

4. Using URN:ISBN, find out if the PDF edition of the book is the 
earliest (most authentic) digital edition of the book, and if not, what 
changes in the look and feel & content are there, compared to the 
earliest version

The starting point is something stable such as a work (or its author) or 
its manifestation which can get an identifier. From there it will be 
possible to proceed in various ways, depending on the users' needs.
>
> Again, when we talk about persistence of a URN, we're not talking 
> about whether the results are the same from one reference of the URN 
> to the next, we're talking about whether the meaning of the URN changes.

Since query is not part of the URN, what is being identified does not 
change. In that sense the meaning of the URN does not change. But each 
example above would use different queries to ask the URN resolver to 
launch different resolution services.
>
> The problem with having a URN that contains a query string be 
> persistent is that it's hard to nail down, in technical terms, what it 
> means for a query to be persistent across all possible query 
> strings.    And to me the simplest answer seems to be that while the 
> base URN is expected to be persistent, a URN that contains a query 
> string (or for that matter a fragment ID) has no assurance of 
> persistence.
Since URN resolution services are dependent on technical infrastructure, 
there may be cases when the required service cannot be supplied. But 
generally speaking adding a query should have no impact on persistence 
of the URN. If the URN is actionable at all, there is always at least 
one service available which could be specified by a query (such as e.g. 
?s=U2R if the resource itself is required).

Juha

>
> Keith
>
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-- 

  Juha Hakala
  Senior advisor

  The National Library of Finland
  P.O.Box 15 (Unioninkatu 36, room 503)
  FIN-00014 Helsinki University
  tel +358 9 191 44293