I'll clarify. There is sometimes such a thing as rft.identifier. :)   
the rft.* values belong to a specific declared OpenURL metadata format. 
The DC one does have an "identifier". That's why you see it in the COinS 
generator for 'generic' items.

However, the DC one isn't typically used for books, journal articles, 
and journals, and if it were used for those there's be no good way to 
include certain significant data that you can include with the 'book' 
and 'article' formats.

rft_id, however, is part of OpenURL regardless of metadata format being 
used in the particular context object, and you can always use it.

Hope this helps. OpenURL is... kinda a mess.

Jonathan

Jonathan Rochkind wrote:
> There is no such thing as rft.identifier.
>
> There is an rft_id  -- it's with the underscore, not a period, because 
> it's not a data element in a _particular_ OpenURL format, rather it 
> applies to any OpenURL format.
>
> rft_id can be set to any URI (although that URI does need to be itself 
> URI-encoded, confusingly).  Typical uses are for an OCLC number or an 
> LCCN. 
>
> I use rft_id to represent my own local accession numbers. First I 
> represent them as a URI: http://catalog.library.jhu.edu/10001.
>
> Then you need to URI-encode that to put it in the KEV OpenURL such as is 
> the basis of COinS:
>
> rft_id=http%3A%2F%2Fcatalog.library.jhu.edu%2F10001
>
> That's probably the best solution you are going to get out of 
> OpenURL/COinS. Yes, it is annoying in a few different ways.
>
> Jonathan
>
> Chris Catalfo wrote:
>   
>> Hi all,
>>
>> I am trying to find the best way to include an item's accession number (i.e.
>> ILS system id) in a COiNS span.  This is in the context of library catalog
>> pages where I'd like to be able to retrieve the ILS accession number to
>> return to LibraryThing for Libraries.
>>
>> I see no mention of an rft.identifier key/value pair on the COiNS site's
>> brief guide to books [1].  It does, however, appear as an element in the
>> COiNS online generator for generic items [2].
>>
>> Googling returned a couple of results using rft.identifier to hold urls.
>>
>> Can anyone enlighten me as to whether using rft.identifier to hold the ILS
>> accession number is valid?  Or suggest a more suitable key/value pair?
>>
>> Thanks for any help you can provide.
>>
>> Chris Catalfo
>> Programmer, LibraryThing
>>
>> [1] http://ocoins.info/cobgbook.html
>> [2] http://generator.ocoins.info/?sitePage=info/dc.html&
>>   
>>     
>
>