UML does not provide a dedicated diagram type in order to express different aspects of concurrency
- instead, concurrency aspects are incorporated into existing diagram types, in particular into behavior diagrams
Active objects are represented using rectangles with bold border lines
- in sequence diagrams, in addition, the whole lifeline is depicted as activation
- in collaboration diagrams, different objects sharing a certain process can be grouped together using a bolded rectangle
Implementation alternatives for active objects:
- heavyweight processes: own address space
- lightweight processes (threads): common address space