Modeling Guide
Knowledge Guides /State machines, activity flows, or sequence diagrams: which should an MBSE project use?
Last updated: · New Horizon Digital Outsourcing Team
The three representations address different questions: state machines describe modes and transition conditions, activity flows describe work steps and branches, and sequence diagrams describe message ordering among participants. Combine them around review questions, avoiding duplicate diagrams of the same workflow that evolve into inconsistent behavior descriptions.
Start modeling from equipment operating modes
- Modes such as standby, running, paused, and fault require entry conditions, exit conditions, and permitted operations. First identify prohibited transitions, such as executing actions before initialization is complete. Mode names alone do not define implementation; specify the triggering event and who confirms completion.
Use activity flows for task decomposition
- Activity flows express parallelism and exception branches for steps such as acquisition, processing, validation, and submission. Define each step's inputs, outputs, and responsible entity. Do not cram every complex algorithm detail into one overview diagram. Expand subprocesses separately while retaining their invocation relationships.
Use sequences to check interface coordination
- Choose a cross-module path and list requests, responses, timeouts, and cancellations. Check whether waiting conditions cause mutual blocking and whether repeated requests cause duplicate execution. Ordering constraints in diagrams must agree with state transitions. Resolve conflicting behavior rules before polishing the diagrams.
How to accept behavior models
- Walk through normal startup, user cancellation, communication interruption, and fault recovery individually. Record triggering events, expected states, and outputs, linking results to verification cases. A behavior model that explains successful paths but cannot explain fault recovery is unsuitable as a complete design baseline.