ISO 29148 and MBSE: Field report by Geoff Shuebrook

ISO 29148 should be familiar to anyone who deals with requirements. Geoff Shuebrook shared how this fits in with MBSE in an INCOSE webinar this week. The core idea is property-based requirements. Geoff also shows how this concept can be implemented in Cameo (MagicDraw).

Below is a summary of this exciting idea and the link to the video and other materials.

Geoff Shuebrook

Geoff has decades of experience as a systems engineer. He is currently a Senior Systems Engineer at Lockheed Martin, where he has worked for 13 years. He focuses on modeling and testing.

In his webinar, he draws on this enormous wealth of knowledge, which consists of both theory and many years of practical experience. This article is merely a superficial summary. His one-hour INCOSE presentation on the content described here is available at Youtube to find.

Core concepts of ISO/IEC/IEEE 29148

The important ISO standard 29148 does not assume that all requirements are available in text form, but this is the focus of the standard. Whether models can completely replace requirements is not up for debate. However, the fact that models and requirements complement each other well I already wrote more than five years ago.

With this in mind, Geoff examined the standard for core ideas that could serve as the basis for an integrating concept. He identified the following three:

• Controlled vocabulary - The standard requires that "all terms should be formally defined and consistently applied".
• Concept model - The standard calls for criteria as "measurable qualitative or quantitative properties that are defined for a requirement."
• Patterns & properties - The standard gives examples of Record templateswhich are filled with properties (among other things).

These concepts are independent of whether we work with natural language or with models.

Semiotic triangle

Another foundation for Geoff's approach is the Semiotic triangle:

Watch out! "Symbol" is usually a word that would typically appear in a glossary, but not the meaning of the symbol. Only the "term" gives the symbol a meaning.

In both requirements engineering and modeling, we like to skip the term, assuming that the meaning is obvious. This is pragmatic and often unproblematic, but also harbors the risk of misunderstandings.

Works by Giancarlo Guizzardi and Patrice Micouin

In order to bring together the identified concepts of ISO 29148 and the semiotic triangle, Geoff drew on the work on conceptual modeling by Giancarlo Guizzardi. Guizzardi is primarily concerned with unambiguous and consistent communication based on the semiotic triangle.

Patrice Micouin is the author of the book Model Based Systems Engineeringwhich also contains the description of a property-based requirements method. The paper Requirements Management within a FullModel-Based Engineering Approach by Yves Bernard provides a good overview.

Property-Based Requirements in MagicDraw/Cameo

The practical application is now exciting. Geoff gave a live demonstration of how property-based requirements in Cameo can be modeled. This is in the video from the 30th minute to see.

Of the three cornerstones of the semiotic triangle, two remain relatively constant, namely the controlled vocabulary and the concept model. Geoff proposes to develop these carefully and store them in a repository to enable reuse. Following this philosophy, he also proposes blocks (classes) for the symbols and block instances (objects) for the things.

In Cameo, Geoff shows a concrete example from the Automotive engineeringwhich is based on the following requirement:

The clearance between the wheel and the components connected to the wheel must be at least 7 mm over the entire wheel arch.

At first glance, the requirement seems plausible and understandable. However, in order to turn this into a property-related requirement, we must first define all symbols. What is a wheel? What is the wheel arch? Geoff models these relationships in Cameo as ConceptDescriptions with relations and properties. Here is an example of the clearance dimension:

This preparatory work now enables us to work with a clearly defined vocabulary in Cameo.

The model chain and its application can be seen live in the video from minute 48:40 >>

YouTube

The benefits of property-based requirements

Anyone who has watched the video at this point will realize that Geoff has done a lot of preparatory work to be able to formulate these simple requirements in terms of properties. Why the effort?

The real added value comes to light when it comes to verifying the requirement. This is now possible at model level. Cameo can now use model checking to ensure that the requirement (clearance of at least 7 mm) is not violated with the selected components.

To check this, not all properties need to be maintained in Cameo. In Geoff's example, many properties come from Catiai.e. the CAD system.

But model checking is just one of many possible applications of property-related requirements. The clarity of communication alone is a considerable added value for complex developments.

Property-Based Requirements without SysML

Geoff has taken a very pragmatic approach. This includes the choice of Cameo as the platform for implementation. The deployment not only requires the team to know how to use Cameo. It also requires extensive customization and profiling, as well as careful model maintenance. Only large, complex projects (and organizations) can afford and justify this effort.

Watching the video, I couldn't help but think of Valispace think. A central idea in the tool is parameterization, as well as the automatic checking of requirements based on parameters. Without having tried it out, I suspect that many of the concepts examined by Geoff can be implemented with Valispace without having to drag along the entire SysML substructure of Cameo.

Conclusion

Property-based requirements are a charming idea. But ideas are all well and good if the implementation is unclear. Geoff did a tremendous service to the systems engineering community in this webinar by showing a practical way to implement the idea with industry tools. A big thank you for that.

I would also like to mention that Geoff has made all the artifacts (presentation, models, etc.) available to the viewers of the webinar. Since he only puts them online on his private server for a short time, I don't want to post a link here that will quickly become outdated. If you are interested, please ask.

Cover picture: Pixabay