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&
>