SYSML12 — Use cases in SysML are more similar to Requiremetns than Behavioral diagrams

There is a non-normative diagram indicating a hierarchy of SysML diagram types. In this diagram we follow the UML convention of treating Use Cases as behavioral diagrams. The exact reason for this is unclear, and appears to be tied up with collaborations.

However, in SysML system engineers (and many s/w eng in UML) treat use cases as a way of capturing goals, capabilities, purposes, and as a technique to organize (and find) requirements. In this way, it is more understandable to the typical SysML user to treat both Use case Diagrams and Requirements Diagrams as belonging to the same category. I have verified this by teaching SysML to students both ways – and the common UCD/REQ approach is thought to be more understandable.

One approach would be to consider the new category Requirement Diagrams, and Use Case and Text-base Requirements as the individual requirements. Another would be to make a new category of Specification Diagrams and use Use Case and Requirements as the individual types.

The above approach represents a reasonable approach to restructuring this
Diagram Taxonomy. However, this taxonomy is intended to be more of a
conceptual organization of the SysML diagrams, and is not a precise
representation. There may in fact be many ways to categorize the diagrams in a
conceptual and informal diagram taxonomy. As a result, this resolution will add a
clarification to the non-normative Diagram Annex that other diagram taxonomies
can be included, and include the categorizing of the use case diagram and
requirements diagram as an example.