Introduction to the notion
The purpose of the Use case diagram is to express the requirements and, as such, may appear from the outset of the specifications. A new version can be created in the design phase, if a new distribution or formulation of the services provided by the system is proposed.
A project can only be based on a single use case. To obtain a diagram, it is therefore not necessary to inflate it with use cases too minutely described. In the Organization Repository, the purpose of the use case diagram is to give an overall view of the system and the services that it provides for the actors.