Use case diagram, activity diagram, Collaboration diagram.
Use case diagram :
It describes the business environment. Its primary goal is to show the series of events and actions within any given process that will be performed by an actor.
The activity diagram is important because it gives an outline of the work flow within the business as well as the activities and action completed.
For instance with a company, there is likely to be more than one department. In such a case each department, will have different access levels to the system.
So if there’s a Medical, HR and Accounts team they will only have access to screens that relate to each.
The activity diagram will highlight the differences within the departments which will be very helpful for developers when they are designing and coding.
A collaboration diagram, also called a communication diagram or interaction diagram, is an illustration of the relationships and interactions among software objects in the Unified Modeling Language (UML). The concept is more than a decade old although it has been refined as modeling paradigms have evolved.