The definition of UML includes two parts: UML semantics and UML notation.
UML can be defined by the following five types of diagrams.
The first category, Use Case Diagram, describes system functions from the user's perspective and points out the operators of each function.
The second category, Static diagram, includes class diagrams, object diagrams and package diagrams.
The third category, Behavior diagram, describes the dynamic model of the system and the interaction between its constituent objects, including state diagrams and activity diagrams.
The fourth category, Interactive diagram, describes the interactive relationship between objects, including sequence diagrams and cooperation diagrams.
The fifth category, implementation diagram (Implementation diagram), including component diagrams and configuration diagrams.