text=A collaboration is a model element that contains a group of classifier roles that work together to realize a behavior that is specified by an architectural mechanism or pattern. The classifier roles in the collaboration may reference classifiers as their bases, but the collaboration does not own the referenced classifiers. This characteristic distinguishes a collaboration from a package or subsystem and yields two important results. First, collaborations can include classifiers from different parts of the system being modeled. Second, a single classifier can participate in multiple collaborations.