A role can be defined as parametric. A parametric role includes a
parameter which can adopt one of a set of values defined with the role.
For example, the role could be called "sales support" and the parameter could define a set
of regions, such as East, West, and South. Even though there is only one role from a
functional point of view, participants are assigned based on the location parameter.
Parametric roles require an instance because the parameter to be used is defined as an
instance variable. This means that global activities cannot be assigned to parametric
roles.
Restriction: Global activities cannot be assigned to parametric roles.