The /ws/2 documentation says
The following list shows which linked entities you can use in a browse request:
/ws/2/artist recording, release, release-group, work

however, taking a work, such as http://musicbrainz.org/work/84173ee3-dc00-306b-81cf-7bea9ecb9a94
and running this query:
http://musicbrainz.org/ws/2/artist/?work=84173ee3-dc00-306b-81cf-7bea9ecb9a94
returns no results.

Is this a valid request? And if so, should it show the artist of the work?