By Kyle Post, Systems Safety Technical Leader at Ford Motor Company and co-author of the OMG RAAML standard.
Model-Based Systems Engineering (MBSE) is gaining popularity in organizations creating complex systems where it is crucial to collaborate in a multi-disciplinary environment. Being one of the key MBSE components, SysML, an open-source system modeling language, has a good foundation for capturing requirements, architecture, constraints, views, and viewpoints. However, SysML does not provide the constructs to capture safety and reliability information in the system model.
While the various safety and reliability implementations may fit the needs for a specific purpose, there are many instances where information needs to be traced and shared across multiple organizations. These model-based solutions may prohibit direct model sharing between organizations and across the various tools.
The need for a standardized UML profile/library for addressing safety and reliability aspects emerged long ago. We have seen multiple commercial-grade model-based safety and reliability solution implementations developed in recent years and maybe successfully used in practice.
A working group of industry experts at the OMG has been working since 2016 to define a new specification providing the necessary capabilities. One of the key goals for the working group is to reconcile these different approaches to alleviate the industry from repeatedly formulating safety and reliability constructs in their tools.
Their new RAAML Beta Version 1.0 specification defines extensions to SysML needed to support safety and reliability analysis. It provides tool vendors with modeling capabilities to build safety and reliability modeling tools that provide traditional representations (e.g., trees, tables, etc.) while using a modern model-based approach. The spec includes:
- The core concepts and shows how the simple concepts are powerful enough to unite all safety and reliability information across a variety of analysis methods,
- The approach to automating several safety and reliability analyses, which is built on leveraging existing SysML functionalities to ensure that the profile and library is usable with existing tooling,
- Specific safety and reliability analysis methods and application domains that are supported. These include:
RAAML specifies two types of conformance:
- RAAML model interchange conformance. A tool demonstrating model interchange conformance can import and export conformant XMI for all valid RAAML models.
- RAAML view specification conformance. A tool demonstrating view specification conformance shall implement the views specified in the RAAML specification.
The RAAML specification can provide the foundation for various safety and quality engineering activities, including safety and reliability analysis methods. Besides the method support, linkages to the SysML model-of-interest are provided, enabling the analyses' integration and traceability.
The organization of RAAML can facilitate tailoring the methodologies to specific engineering domains and industries to support the various assessment and certification agencies. The RAAML working group uses a library approach heavily with a light UML profile support. Using model libraries has several significant benefits compared with implementing everything in a profile.
The RAAML development uses a model-driven approach. A simple description of the work process is that the specification is generated from the UML model used to describe RAAML. This approach allows the working group members to concentrate on architecture issues rather than documentation production. The UML tool automatically maintains consistency.
The standard uses UML/SysML structural modeling capabilities to capture safety and reliability data. A collection of scenarios and situations captures the safety and reliability data.