Ah right it's ClassificationWeb that has this. Alas, ClassificationWeb 
is both not open (requires a subscription), and also, as far as I know, 
offers no machine API, it's purely manual human access.

This would definitely be an interesting project for someone to do to 
create a source of open data on LCSH/LCC correlations. Somewhat 
challenging, but definitely not 'rocket science' as they say. I think 
the data would be desirable by many.

Also, as I mentioned in another email, some but not all LCSH authority 
records already identify suggested correspoinding LCC's; LCSH authority 
data can be obtained from id.loc.gov among other places.

On 12/10/13 5:02 PM, Bryan Baldus wrote:
> On Tuesday, December 10, 2013 7:18 AM, Irina Arndt wrote:
>> we would like to add DDC classes to a bunch of MARC records, which contains only LoC Subject Headings. Does anybody know, if a mapping between LCSH and DDC is anywhere existent (and available)?
> ...
>> I'm thinking of a tool, where I can upload my list of subject headings and get back a list, where the matching Dewey classes have been added (but a 'simple' csv file with LCSH terms and DDC classes would be helpful as well- I am fully aware, that neither LCSH nor DDC are simple at all...) . Naïve idea...?
>
> Classification Web offers a correlations feature between Dewey and the 1st LCSH, based on usage in LC's database (as well as correlations between LCC and LCSH, and DDC and LCC). It is of some use in helping the cataloger determine possible classifications or subject headings to use. Unfortunately, I don't believe ClassWeb is easily accessible by automated processes (even for subscribers). Even if it were, I doubt it is possible to automate a process of assigning Dewey based on 1st LCSH. As mentioned, the 1st LCSH and classification are generally supposed to be similar/linked, but that applies more to LCC/LCSH than DDC to LCSH, due to the way Dewey works. For example, ClassWeb correlation between LCSH Disease management (chosen while looking at Health, then Disease, then looking for an example showing a better variety of Deweys than the 1st 2) shows DDCs used by LC (counts of records in parentheses):
>
> Disease management [Topical]
>           362.1 (4)
>           610.285 (1)
>           615.1 (1)
>           615.5071 (1)
>           616.89142 (1)
>
> ####
>
> That said, as Ed mentioned, given a large set of records for training, you should be able to develop something to help local catalogers determine possible Deweys record-by-record.
>
> I hope this helps,
>
> Bryan Baldus
> Senior Cataloger
> Quality Books Inc.
> The Best of America's Independent Presses
> 1-800-323-4241x402
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>