Which construct specifies all possible valid traces?

In the OMG Unified Modeling Language (UML) Interaction specification, an assert combined fragment designates an assertion operator. The operand inside an assert combined fragment represents the only valid continuation of the interaction. Any trace of events that does not conform to the interaction specified within the assert operand is considered invalid. Consequently, the assert construct explicitly defines all possible valid traces at that point in the execution sequence, asserting that no other event sequences are valid. This mechanism is crucial for formal verification and specifying strict behavioral constraints where deviations from the designated sequence are explicitly prohibited by the model specification.

A. Generalized ordering defines partial order constraints between event occurrences across lifelines, but it does not specify or restrict all valid traces.

B. The alt fragment specifies alternative paths (choice), where each operand represents a valid trace, but it does not assert that those are the only valid continuations overall.

C. The opt fragment specifies optional behavior that may or may not occur, defining acceptable choices rather than asserting the set of all valid traces.

- Object Management Group (OMG). (2015). OMG Unified Modeling Language (OMG UML), Version 2.5. Section 17.6.3.1 (CombinedFragmentKind - assert), p. 582.

- OMG OCUP2 Advanced Examination Coverage Manual, Section 3: Interactions and Sequence Diagrams.