Robustness analysis was introduced by Ivar Jacobson in his initial books on Use Cases. Robustness analysis involves examining the text or steps of each Use Case and identifying the classes that are needed for the Use Case scenario to be performed. These classes can be categorized into a number of different types: boundary classes, entity classes, and control classes.

You can build a “Robustness Diagram” by graphically adding these classes to a Use Case diagram, and modeling relationships between them. In Jacobson's initial Use Case work, this diagram was called an 'Ideal Object Model'.

The collection of objects garnered from the Ideal Object Models of your system become the basis of your static analysis models of the system (for example, your class diagrams).

Often when building the Robustness diagram, you might want to hide relationships between classes and the Use Case itself to make the diagram less congested and easier to read. To do so in System Architect, right-click any relationship line in the diagram, and then click Hide Selected Relationship Line.