A classification of object types commonly found in
Actors, Agents, Proxies, and Roles
Roles are played/assumed by people or external software agents,
for example Yahoo web crawler).
Agents are objects that perform some task for another.
It can be helpful to create an agent when some operation is
complex or requires state just for that one operation.
The idea is to delegate the operation to the agent.)
Class names for these usually end with "er" or "or":