Very nice, thanks.

I wonder the rationale behind searching both valid and cancelled LCCNs.  
This has caused me trouble in the past in similar systems, because a 
cancelled LCCN seems in some cases to duplicate a different valid LCCN, 
so you search on an LCCN, and get, in this case, both the correct record 
and and an incorrect record -- the requirement that software take 
account of this and look into the records to see which is the valid one 
adds significant complexity to the software, and is also a detail likely 
to be overlooked in client software implementation.

I wonder if any alternatives were considered. I'm not exactly sure what 
the solution is though -- if it wasn't for the _collision_ issue, then 
we could say requesting a permalink for a cancelled LCCN should result 
in an HTTP redirect to the permalink for the correct LCCN.  But a 
cancelled LCCN on one record can be identical to a correct LCCN on 
another, or theoretically the same cancelled LCCN could exist on more 
than one record -- making it unclear what design could be better.

On 9/7/2011 1:55 PM, Della Porta, Ann wrote:
> Apologies for cross posting.
>
> The Library of Congress is pleased to announce an expansion of its LCCN Permalink Service for the Library's name and subject authority records. These persistent URLs are based on the Library of Congress Control Number (LCCN). As with bibliographic records, LCCN Permalinks are displayed on authority record entries in LC Authorities<http://authorities.loc.gov>.
>
> Create an LCCN Permalink
> Simply begin your URL with the LCCN Permalink domain name -- http://lccn.loc.gov/ -- then add an LCCN.
>         Examples:  http://lccn.loc.gov/n79018774   or  http://lccn.loc.gov/sh85026371
>
> LCCNs should be formatted according to the info:lccn<http://info-uri.info/registry/OAIHandler?verb=GetRecord&metadataPrefix=reg&identifier=info:lccn/>  URI specification. Instructions are also available in the LCCN Permalink FAQ<http://lccn.loc.gov/lccnperm-faq.html>.
>
> How LCCN Permalink Works
> An LCCN Permalink retrieves a MARCXML-formatted record using the Z39.50/SRU protocol. Both valid and cancelled LCCNs (MARC 21 fields 010a and 010z) are searched. Authority record displays for LCCN Permalink follow the labeled display found in LC Authorities. MARCXML and MADS versions of the records are also available. Displays link to entries in LC Authorities<http://authorities.loc.gov>  and the LC Online Catalog<http://catalog.loc.gov>  -- and, where appropriate, to entries in the Virtual International Authority File<http://viaf.org>  and LC Authorities and Vocabularies<http://id.loc.gov/>.
>
> More Information
> Additional information on this service is available on the LCCN Permalink FAQ<http://lccn.loc.gov/lccnperm-faq.html>. Specific questions can also be sent to the Library of Congress through Ask-A-Librarian<http://www.loc.gov/rr/askalib/ask-digital.html>.
>
>
> Ann Della Porta
> Chief, Integrated Library System Program Office
> Library of Congress
> Washington, DC 20540-4010
> [log in to unmask]
>