Kelley McGrath <[log in to unmask]>
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.
Then you've got all of those MARC records that don't use ISBD punctuation at all.
Mark K. Ehlert Minitex
Coordinator University of Minnesota
Digitization, Cataloging & 15 Andersen Library
Metadata Education (DCME) 222 21st Avenue South
Phone: 612-624-0805 Minneapolis, MN 55455-0439