What is use case diagram ?

Our exciting project days are starting with Archi's Academy! We used the Use Case Diagrams to set up the structure of our project this week. So what are these Use Case Diagrams and what are they used for?

Use case diagrams are usually referred to as behavior diagrams used to describe a set of actions (use cases) that some system or systems (subject) should or can perform in collaboration with one or more external users of the system (actors). A UML use case diagram is the primary form of system/software requirements for a new software program underdeveloped.

In brief, the purposes of use case diagrams can be said to be as follows − Used to gather the requirements of a system. Used to get an outside view of a system. Identify the external and internal factors influencing the system. Show the interaction among the requirements are the actors.

It was very useful for me to gain experience with UML use case diagrams. Well, have you ever used these diagrams?