A use case diagram in the Unified Modeling Language (UML) is a type of behavioral diagram defined by and created from a Use-case analysis. Its purpose is to present a graphical overview of the functionality provided by a system in terms of actors, their goals (represented as use cases), and any dependencies between those use cases.The main purpose of a use case diagram is to show what system functions are performed for which actor. Roles of the actors in the system can be depicted.