[Metadatalibrarians] MODS "smd" question

[Greta de Groat]

Hello all,

I'm puzzled by the MODS physicalDescription form attribute for "smd."  I
see that there is a list here:
http://www.loc.gov/marc/sourcecode/form/smdlist.html

But i am puzzled.  In my experience as a traditional cataloger, smd to
me means the specific material designation that's put in MARC field 300
$a and comes from AACR2.  The above list was derived from the MARC 007
field, which has never completely described the universe of materials.  
Is it that we are only to use the values on that list and not the values
in AACR2 x.5 fields?  There are values there that are not on the list,
(such as sound files, electronic text, and optional "terms in common
usage" such as CD-ROM and DVD-ROM),  and the values that are there
aren't in the same form (such as tape cassette vs. computer tape
cassette, or regular print instead of v.).

What if one is creating the MODS record only for the electronic
manifestation of of something, without reference to the analog original
(or a born-digital item, for that matter).  It appears that we would use
form authority="marcform" electronic, but the form field with
authority="smd" may only be for the original format?  If we don't care
about the original format would we just omit this and rely on the
Internet Media Type field to relay the information about the fact that
it's some sort of digital file?   I suppose one could call everything
"remote" but that seems unhelpful.

And in most MODS records i see, the extent field uses the AACR2 smd
terminology.  Would i be able to use, say, 3 sound files as the extent,
since that appears as a permissible formulation in AACR2?

thanks
Greta de Groat
Stanford University Libraries