UML There are two kinds of models , Dynamic model and static model . Use case diagram , Both class and object diagrams are UML Static structure model in . And in the UML One of the system dynamic models is interactive view , It describes the sequential relationship between the roles that perform system functions to pass messages to each other . Sequence diagram is a form of interactive view .
Sequence diagram is a visual representation of the time sequence of messages transmitted between objects . The main purpose of sequence diagram is to express the requirements of use cases , To further , More formal level of fine expression . Use cases are often broken down into one or more sequence diagrams . At the same time, sequence diagram can more effectively describe how to assign the responsibilities of each class and the reasons why each category has corresponding responsibilities .
Sequence diagram （Sequence Diagram） By object （Object）, lifeline （Lifeline）, activation （Activation）, news （Messages）, It is composed of branches and subordinate flows .