Write scenario for each use case in the use case model. Use each scenario for searching all objects needed for this scenario realization. Each from these objects will have their time line of living in interaction diagram - sequence diagram (SEQD). Analyze collaborations between objects in time of realization specified use case. Each collaboration needs communication - interchange of messages between objects. Reaction on received message can be some operation on the side of receiver (operation realized by receiver). This operation can be defined with use of member function of classes (methods). Describe all messages in SEQD with use of name of message (id of message) and content (arguments). Choice suitable operation from list of member functions of class (all needed such functions have to be previously defined in classes). Identify who/what (object) is sender and who/what (object) is receiver of this message. Important is time sequence of messages, time flow from top to down in SEQD. Another view of behaviour of objects is based on modeling of communications between objects (collaborations) - collaborations can be modeled by collaboration diagram (COLD) or communication diagram (COMD). If we have already created SEQD, it is possible change view from SEQD to dual COMD.

Find classes with objects which are characterized with several states in their life cycles. Each state of object differs from other states by different values of state variables and by different ability to react on events. Modeling of states for critical objects in modeled system can formally describe behaviour of these objects.