1. Use Case Diagram describes interaction between user and the system.
2. Use Case Diagram doesn’t tell detailed information about individual feature of the system, it is used to describe the complete functionality of the system.
3. Use Case Diagram is suited to describe high level functionality of the system, it is not recommended to use where we have to capture the entire flow of the system like number of hits to a particular module or exceptions etc.
4. Use Case Diagram has four major elements
• Actors: A role that a user plays with respect to the system,including human users and other systems. e.g.,inanimate physical objects (e.g. robot); an external system that needs some information from the current system.
• Use Case: A set of scenarios that describing an interaction between a user and a system, including alternatives.
• System boundary :A rectangle diagram representing the boundary between the actors and the system.
• Relationships: The lines between the elements
5. How to identify actors in Use Case Diagram?
Elements whose behavior appears in actors actions column are actors, it may be humans or system interacting with other system example: cronjob interacting with a database for updating user information here cronjob is a process which is actor in Use Case Diagram because it interacts with the other system which is database here other example for humans online banking here humans are actors because they are interacting with the banking system to get there work done by sending a request to the system.
6. how to identify systems in Use Case Diagram?
Elements whose behavior appears in System responses column are components in the system, system box contains use cases one for each service that the system provide to the actors, any internal behavior of the system that the other parts of the system uses should not appear in system box