PURLs

[weibel at oclc.org]

 Marc Salomon writes:
 
> persistence is but one slice of the larger (largest?) problem. 

  Marc is exactly right.  PURLs, by providing an additional level of
  indirection, are intended to be only *one* component of an incremental
  solution to the larger problem.  The larger problem requires the 
  evolution of services that librarians will recognize as cataloging
  systems applied to networked resources.
 
> replication is equally as important for certain documents.  one problem
> i have w/purls was that it was a one-to-one mapping of purl->url, and
> for many applications this hinders scalability. why can't a purl server
> respond with multiple uri: fields pointing to replicated documents and
> the client can decide which to retrieve?

  Marc's replication issue is important, its just not the problem that
  PURLs are intended to solve.  Our view is that even with a complete
  URN solution, resolution should return *exactly* one URL. 
  
  Choosing a URL among several alternatives can be made according to
  political, technical, geographical, and economic factors.  Might not
  servers be a better place than browsers to implement such decisions?
  Besides, keeping a marketplace of browsers in sync (indeed, changing
  them at all) is not a happy prospect.  

  Among the virtues of PURLs is that they work now, with no modifications
  to browsers.  tools to manage the replication problem can be built on
  top of PURLs.

> can a client/proxy cache the location: <url> as a substitute for the
> original one or will you use the moved temporarily http response code, 
> and if the latter doesn't this present scaling problems as you double 
> the number of transactions required to fetch each request?

  The PURL server returns a URL to the client, which the client fetches
  in a conventional manner, and caches normally.  

> but i do think that this is a good first step towards experimenting with a
> level of indirection in web document access.

  Thanks!  Stop in at http://purl.oclc.org and get a PURL for your homepage.