The practical application of traceability Part 3: What’s really going on when V&V leads to new requirements?
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In this guest blog post, Requirements Engineering Expert, Jeremy Dick continues with his discussion on practical applications of traceability. Read the first two parts here.
Inspired by recent experience in a large systems engineering project, Part 1 of this blog post series covered the practice of decomposing requirements, which brings about one of the most important traceability relationships in requirements engineering. Part 2 covered the next most important relationship: that between requirements and validation and verification activities.
Part 3 (probably the final part!) presents some other things about V&V we think we have learnt from undertaking a large project: what do you do about new requirements that arise from the V&V you have planned against your main requirements?
Once the need for V&V activities has been established (see Part 2), this will often give rise to new requirements. Broadly speaking, these requirements fall into two types:
Neither of these types of requirement should really be mixed in with the remaining requirements of without recording (through traceability) their origin, because if the choice of V&V changes, then we should be able to identify which parts of the design – or which pieces of test equipment – are present only to make the old V&V possible.
If the need to test a product gives rise to the need to build facilities to carry out that testing, then another development life-cycle is spawned for the purpose. Requirements will be collected for the facility, and further V&V may be required against those requirements. We enter a sort of recursive world of development life-cycles. Some call this “fractal” – the main development spawns smaller developments, which in turn spawn yet smaller ones.
Primary versus Secondary V&V
Secondary V&V arises when V&V activities lead to test artefacts that also need validating or calibrating. For example, from requirements about power delivery, there is a direct need to do some analysis using a model of fluid dynamics – what we call primary V&V. Requirements for the model itself are collected, and the need for validation of the model considered. For example, the model may need calibrating against some similar existing systems. This calibration activity is another form of V&V – what we call secondary V&V.
Requirements lead to V&V activities lead to requirements
As noted above, the need to for V&V leads to design changes or secondary systems, and thus to further requirements. This relationship should be captured; a requirement, rather than having a parent requirement, may in fact have a parent V&V activity. We could say that a requirement “enables” a V&V activity.
In the extreme, a secondary system may impose requirements on the primary product, for instance through the need to interface with it.
An information model
The diagram below illustrates the idea that requirements enable V&V activities
In the diagram, three traceability relationships are shown: “satisfies”, “verifies” and “enables”. There is an example of a primary V&V activity leading to an enabling requirement on the primary system itself – a requirement whose parent (through the “enables” relationship) is a V&V activity.
There are also two examples of secondary systems driven by requirements for primary V&V, and one of those gives rise, in turn, to a tertiary system.
In our current project, we have pushed this model only as far as secondary systems with an “enables” relationship and secondary V&V. An example is the one cited above – a fluid dynamics model that needs itself to be validated through calibration with similar existing systems.
As with all these things, there is probably a law of diminishing returns. How far should you push the requirement to V&V to requirement to V&V to requirement chain? You will have to decide!
A similar model probably exists for other aspects of development – manufacture, for instance. The need to manufacture a product gives rise to the need to construct the factory and plant to do so – a primary development spawning a secondary development. However, the traceability train goes not from requirement to V&V activity to requirement, but rather directly from primary requirement to secondary requirement. This could still be characterized as enablement.
We never build just “the product”. There are always other things that need designing and building that surround the system for various purposes, including testing components, sub-systems, systems and completed products.
What has been presented here is an attempt to get to grips with the traceability required to track the relationships between the product and its secondary (and possibly tertiary) systems.We implemented all this in a Rational DOORS database, with a small amount of customisation to ease the way.
Thank you for reading these blog entries, and please contact me if you are interested in reusing any of this experience and associated Rational DOORS customization.
Read the first two parts here -
About the author - Jeremy Dick works as Principal Analyst for Integrate Systems Engineering Ltd in a consultancy, research and thought leadership capacity. He has extensive experience in implementing practical requirements processes in significant organizations, including tool customization, training and mentoring. At Integrate, he has been developing the concept of Evidence-based Development, an extension of his previous work on “rich traceability”. Prior to this appointment, he worked for 9 years in Telelogic (now part of IBM Rational) in the UK Professional Services group as both an international ambassador for Telelogic in the field of requirements management, and a high-level consultant for Telelogic customers wishing to implement requirements management processes. During this time, he developed considerable expertise in customizing DOORS using DXL to support advanced engineering processes. His roles in Telelogic included a position in the DOORS product division to assist in the transfer of field knowledge to the product team. Co-author of a book entitled “Requirements Engineering” that has recently reached its 3rd edition, he is recognized internationally for his work on traceability. Jeremy can be reached out at jere