Requirements Management 101 (4/6)

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What is traceability? Or more specifically what is requirements traceability? Well rather than repeat what is already a good collection of definitions, I’ll refer you to http://en.wikipedia.org/wiki/Requirements_traceability.

From there I’d summarize three elements to requirements traceability:

  • Following the life of a requirement – from idea to implementation
  • How requirements impact each other, and how requirements impact other development lifecycle artifacts (such as designs, tests, tasks, source code, hardware specs, etc.) and vice versa.
  • The decomposition of requirements – from high level user/customer/market needs to system, sub-system, software or hardware component requirements; and transformation into design specifications and the implementation realization of the requirement.

Traceability in this context is about relationships between requirements at the same or different levels of detail, and between requirements and other lifecycle artifacts as listed above. It also extends to relationships beyond those directly involving requirements – i.e. the relationship of a defect report to a test case – this is referred to as ‘lifecycle traceability’. Traceability relationships can be of multiple types, for example:

  • Satisfaction: a system requirement (or more likely a number of system requirements) ‘satisfies’ a user requirement.
  • Verification: a test case ‘verifies’ a requirement.
  • Dependency (often used where interfaces are concerned): a requirement ‘depends’ on another requirement.

Basic traceability establishes a relationship or link between one or more elements. Typed traceability adds the relationship type with its associated semantics. Rich traceability adds additional information on the traceability relationship such as the rationale explaining why a group of systems requirements satisfies a particular user requirements; or as is often the case, you can’t be 100% certain on specification or design decisions, you might document any assumptions you made in deriving a set of systems requirements from a user requirement. The rich traceability approach is particularly valuable in heavily regulated industries and safety-critical systems where audit trails of decisions made are vitally important to provide assurance and reduce risks.

Once traceability has been established there are multiple ways in which it can be viewed and reported on. Perhaps the oldest and most commonly recognized method is the traceability matrix where you can see the intersection between two sets of requirements and a check or cross shows where a link exists. This method doesn’t scale particularly well since the matrix could become very large. It’s also sometimes used for creating the links, but it’s not ideal for that either since you can typically only see a small amount of information on the requirements.

Another way to see traceability is to pick a starting point, e.g. the user requirements and display the related systems requirements alongside the user requirement they are linked to, in a traceability column. You can typically choose how much detail of the linked requirement is displayed, and you can even make it recursive, going down as many levels of requirements as you need/is practical to manage in a single view.

Graphical displays are great for getting a bigger picture view of traceability rather than immediately focusing in on the details of particular relationship. You can explore the traceability tree, zooming in/out or collapsing/expanding parts of the tree, or changing the focus (starting point) of the tree.

Hereby a few resources below that I’d recommend you take a look at for getting a better understandinf of Requirements Traceability:

Next topic will highlight what traceability can be used for.

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