SDL Simultaneous Event Handling Without Defined Ordering Constraint

SDL Simultaneous Event Handling Without Defined Ordering Constraint

Goal: obtain deterministic simulation results when multiple events are queued at the same instant in an SDL model.

Constraint: the SDL specification does not prescribe an execution order for simultaneous events, leaving the behavior to individual tool implementations (e.g., FIFO, LIFO, priority‑based queues).

Uncertainty: because the ordering is unspecified, different SDL tools may produce divergent transition sequences, which can affect verification and validation efforts and hinder model portability.

• What ordering mechanism should be standardized to ensure deterministic SDL simulation?
• Which approach—explicit event priority annotations or tool‑defined defaults—best resolves the simultaneity ambiguity?
• Can modelers rely on tool documentation to determine the implicit ordering used for simultaneous events?