From: Program for Cooperative Cataloging [mailto:[log in to unmask]] On Behalf Of Stephen Hearn
Sent: Monday, December 11, 2017 2:37 PM
> The relationship that RDA expects to be represented hierarchically in the AAP string is
> the relationship between the work and an expression. There is no relationship designator
> for the relationship between a work and an expression ...

No designators, but we do have the elements in RDA Chapter 17 and their labeling to make the relationships clear:

100 1 $a Gregorovius, Ferdinand, $d 1821-1891. $t Lucrezia Borgia. $l German $s (Third edition)
500 1 $i Work expressed: $a Gregorovius, Ferdinand, $d 1821-1891. $t Lucrezia Borgia $w r

That said, I haven't come across any authority records making use of these elements--putting NACO practice and record maintenance aside, the Work AAP is already embedded in the Expression AAP in a kind of shorthand, as Stephen notes above.  But this can be different in Bibframe or another non-MARC coding environment:

bfWork record describing an RDA Work
<work expressed> / <expression of work>
bfWork record describing an RDA Expression

As we move into linked data record/data formats, is it worth the effort to begin denoting Chapter 17 relationships *explicitly* in MARC authority records?

Mark K. Ehlert                 O'Shaughnessy-Frey Library
Cataloging and Metadata        University of St. Thomas
  Librarian                    2115 Summit Avenue
                               St. Paul, MN 55105
- Alma: NA02 // Primo: MT NA01

  "Experience is by industry achieved // And perfected by
the swift course of time"--Shakespeare, "Two Gentlemen of
Verona," Act I, Scene iii