RUP activites across multiple roles?

Hi,

Is there a way, in workflow modeling, to represent an activity
performed by many roles? For example, let's say a development team is
performing a "detail analysis" of some requirements in a "group
discussion". This involves a business analyst, a senior developer and
a QA member. So we have an "activity" with 3 "roles" involved. How can
we model this in a digram which models the "roles" as horizontal bars
with a "worker" icon in front?

Or is it a must to have a one-to-one mapping between activities and
roles? If so, what is the correct way to model the above example?

Cheers,
Ishan.

.