Wouldn't it be better to just use the markup or field label to tell
you whether the value is a parallel title, subtitle, second title,
etc.?  The punctuation doesn't mean anything to non-catalogers and it
isn't consistent in any case, since not all who code this information
know how to punctuate it "correctly".  Look at some of your
vendor-created e-book, approval, patron-driven, etc. records or your
locally-created reserve material records if you don't believe me.  Not
that I expect folks to correctly label the markup either, but at least
that makes more sense than relying on arcane markings known only to
members of the guild.

     Charley

On Tue, Jan 29, 2013 at 10:25 AM, Kelley McGrath <[log in to unmask]> wrote:
> Like many things, this is not so simple in practice. The meaning of 245$b depends on the preceding subfield (often, but not always $a). Preceded by : it's a subtitle. Preceded by = it's a parallel title. Preceded by ; it's a second title (another work) by the same person or people as the title in $a. In addition, you can have ISBD punctuation within the subfield for parallel titles or more titles by the same person/people.
>
> Kelley

-- 
Charley Pennell
Principal Cataloger
NCSU Libraries
North Carolina State University