Behavior Diagrams for Model-Based Systems Engineering (MBSE): Activity Diagrams
From the series: Behavior Diagrams for Model-Based Systems Engineering (MBSE)
This first part in the MBSE Behavior Diagram series focuses on activity diagrams, which represent the flow of data between system functions and their interactions. These diagrams break down high-level activities into actions and sub-actions, using control flows and data tokens to depict the sequence and data movement. By creating executable activity diagrams in System Composer™, engineers can validate and refine system requirements, saving valuable time and reducing rework.
Published: 12 Aug 2024
Behavioral diagrams are a key advantage of model-based systems engineering, providing engineers with a method of visually describing the system dynamics and how it should interact with its environment. System Composer is tightly coupled to a modeling and simulation engine, greatly increasing the effectiveness of those diagrams and helping to create implementable requirements and convey design intent to downstream functional teams.
In this video, we will review activity diagrams, when to use them, and how employing them in System Composer helps to ensure system engineering and design processes remain in sync. At the most abstract level, a system is comprised of the minimum set of functions needed to accomplish a desired outcome. Because of this, many systems engineers start the development process by creating a functional decomposition of the system, breaking down complex system functions into their simpler constituents.
As the functional decomposition matures, activity diagrams are often used to describe the dynamics and interactions of system functions and the flow of data, similar to a flow chart. These are commonly referred to as actions. Control flows represent the order in which the actions are executed in the absence of data, whereas object flows represent the data being moved between actions with a data token.
Pins are placed on the actions to provide entry and exit points for object flows and associated tokens. Pins placed at the root level of the activity diagram are referred to as parameters. Control nodes can be used to branch, merge, or add conditional logic to the flows between actions.
In this way, high-level activities are composed of a set of actions. Actions can be decomposed into subactions or call an external behavior or script, allowing you to make use of MATLAB and all available toolboxes to further describe and simulate your action.
Beyond just creating descriptive images, activity diagrams in System Composer gives you the ability to construct dynamic executable diagrams with a traceable digital thread back to your requirements and models. Just like in architecture models, you can allocate between activity elements, other activity elements, and architectural elements. Link and annotate requirements to your activities to establish traceability. And generate reports to share your models with external stakeholders.
By creating activity diagrams that are executable, you can simultaneously validate and refine your system architecture and requirements, saving valuable program time with early validation before moving into detailed design. This is just a small overview of what is possible with activity diagrams in System Composer. If you'd like to learn more, check out our Solutions page or one of our examples. And don't forget to check out our other behavior diagram videos. Thanks for tuning in.