Hi, I'm interested in mapping the LCSH topics described in Library of
Congress book records to the "predefined headings" LCSH thesaurus
defined at http://id.loc.gov.

For example, the MODS version of the LoC record for isbn 1606238760
contains this LCSH info:

  <subject authority="lcsh">
    <topic>Social sciences</topic>
    <topic>Statistical methods</topic>
    <topic>Data processing</topic>
  </subject>

... which maps neatly to "sh2010113695" (Social sciences--Statistical
methods--Data processing) (see
http://id.loc.gov/search/?q=Social+sciences--Statistical+methods--Data+processing&q=)

However, not all topics map to a single shNNNN code (multiple shNNNN's
with the same description), and some topics have no shNNNN code at
id.loc.gov (e.g. "Discourse analysis--Research", even though
"Discourse analysis" exists)

Is there a way to retrieve the shNNNN codes directly for a book
record? I'm currently using the LoC SRU (search/retrieval via URL)
service, but it only serves verbose, "textual" <topic>s that must be
mapped separately to a shNNNN code (when possible)

Thanks,
Dan