The first step in building a use case diagram is to add a figure representing the boundaries of the library catalog system. This boundary separates the use cases (which are essentially part of the system) from the actors (which are outside the system).
To add a new figure to the diagram, you first create the figure and then attach it to an underlying model element. A system figure must be attached to a group element, which we have not created; in this case, therefore, we will be adding a node figure and creating an underlying model element simultaneously.
To add a system figure, follow these steps:
When first added to the drawing surface, the icon is labeled with a
question mark. This indicates that it is not yet associated with an
underlying model element. All elements in UML Designer diagrams must be
associated with underlying models.
A group is an organizational element you can use to collect related model elements together. In a use case diagram, a group is the underlying model element for the system figure, which is essentially a grouping of related use cases.
The system figure is now attached to the new group, and the label
Library Catalog appears in the diagram.