We are mapping data to MODS record structures (from a PICA library system via Marc21 interface) . This includes various kind of authority data, eg. subjects, persons etc. For subjects, the authority data is in SKOS. (Thesaurus for Economics, preview on http://www.zbw.eu/beta/stw). It is based on concepts with an URI as persistent identifier. The concepts have prefered labels in German and English, which should be present in the MODS records for display and indexing convenience.
What we figured out as a possible solution is this:
<subject authority="stw" xlink:href="http://zbw.eu/stw/descriptor/19664-4" lang="en">
  <topic>Financial crisis</topic>
<subject authority="stw" xlink:href="http://zbw.eu/stw/descriptor/19664-4" lang="de">
(We don't really like the de-normalized form. Much better would be:
<subject authority="stw" xlink:href="http://zbw.eu/stw/descriptor/19664-4">
  <topic lang="en">Financial crisis</topic>
  <topic lang="de">Finanzmarktkrise</topic>
However, that's invalid in MODS 3.3)
What do you think - is it ok to use xlink:href for the reference to the authority record?
Since we are new in the MODS field, we wonder if there is are other solutions or best practices for this we may not be aware of.
Cheers, Joachim
Joachim Neubert
IT Development
German National Library of Economics (ZBW)