Sunday, April 09, 2006

Extreme Traceability

I gave the following response in a March 24 posting to the extreme programming list on the subject of XP-style traceability:

dsrkkk wrote:
Whatever process we use, we need to track requirements, user stories to design and test cases. The traceability provides obviously many benefits. Why don't we automate traceability? How can we humanly track these complex relationships? If we do manually, we may miss something.
I responded . . .

The less you work in a waterfallish-way, and the more you work in an agile fashion with very short feedback loops, the less necessary it becomes to make additional efforts to track/trace requirements.

If I first do lots of requirements, then lots of design, then lots of code, etc., I have to "put the pieces together." The task I performed to write requirements was different from the one that did the design which was different from the one that did code, tests, etc.

If I work in very short cycles (particularly using test-driven development), then an individual development task looks something like:
  • write a single test
  • write the code to pass the test and no more
  • refactor the code
  • commit my changes (Note I might commit my changes before refactoring too).
If, when I commit my changes to the repository, I associate my "commit" with the name or id of the story the test was for, then I have a single, fine-grained change-task that went thru the complete cycle of specification, implementation/design, verification all in a matter of minutes for a single "commit" and user-story.

Working in such fine-grained full-lifecycled tasks automatically associates all the elements that were created & updated as part of the task, which in turn is associated with a user-story. Ta da!!!! Traceability comes along for the ride almost automatically.

From Extreme Locality, in the Feb 2004 "Agile Times", pp.37-40
In Agile methods, we often hear a lot about the importance of simplicity: simple design; do the simplest thing that could possibly work; simple tools; minimal documentation ... Much of the documentation and artifacts created in larger software development methods is for the sake of capturing historical knowledge: the rhyme and reasons behind why something is there, or is designed a certain way.

The desire for such information is often used to justify the need for formal traceability and additional documentation for the sake of maintainability and comprehension. Some very powerful and sophisticated tools exist to do this sort of thing. And yet, there are basic fundamental principles and simple tactics to apply that can eliminate much of this burden.

The mandate for formal traceability originated from the days of Department of Defense (DoD) development with very large systems that included both hardware and software, and encompassed many geographically dispersed teams collaborating together on different pieces of the whole system. The systems were often mission critical in that a typical “bug” might very likely result in catastrophic loss of some kind (loss of life, limb, livelihood, national security, or obscenely large sums of money/funding).

At a high level, the purpose of formal traceability was three-fold:
  1. Aid project management by improving change Impact Analysis (to help estimate effort/cost, and assess risk)
  2. Help ensure Product Conformance to requirements specs (i.e. ensure the design covers every requirement, the implementation realizes every design element and every requirement)
  3. Help ensure Process Compliance (only the authorized individuals worked on the things [requirements, tasks, etc.] they were supposed to do)
On a typical Agile project, there is a single team of typically less than two-dozen. And that team is likely to be working with less than 10 million lines of code (probably less than 1 million). In such situations, many of the aforementioned needs for formal traceability can be satisfactorily ensured without the additional rigor and overhead of full-fledged formal requirements tracing.

Rigorous traceability isn’t always necessary for the typical Agile project, except for the conformance auditing, which some Agile methods accomplish via test-driven design (TDD). A “coach” would be responsible for process conformance via good practices and good “teaming,” but likely would not need to have any kind of formal audit (unless obligated to do so by contract or by market demand or industry standards).

Agile methodologies turn the knob up to 10 on product conformance by being close to the customer, by working on micro-sized changes/increments to ensure that minimal artifacts are produced (and hence with minimal reconciliation) and that communication feedback loops are small and tight. Fewer artifacts, better communication, pebble-sized change-tasks with frequent iterations tame the tiger of complexity!
For more then you ever wanted to know about the why&wherefore behind traceability, see The Trouble with Tracing: Traceability Dissected

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