I’m at the start of a new project. We’re currently determining what features are needed in the end-product. This has led to me to thinking a lot lately about how to capture, prioritize and track the completion of these requirements as we progress through the project. Of course, I want to do this in an ‘agile’ way.
The typical agile method is to capture requirements in a set of high level “users stories”. User stories typically provide a concise way of describing what the system will do from the user’s perspective. Several templates of a user story exist; Mike Cohn’s being the one that I think is clear and concise:
As a <type of user>, I want <some goal> so that <some reason>”.
It captures the who, the what and the why of a feature – providing some essential context to the assist in the implementation, validation and acceptance of a feature.
User stories are then typically split into progressively smaller use-cases, or tasks until you establish a firm understanding of what the feature is supposed to do, and how your team is going to complete the functionality as the user expects.
I found Cohn’s template particularly effective when creating some tool or script that I needed to create because it is much easier to comprehend than a typical requirement statement of “The system shall….”.
But… if there’s one aspect of agile that I really think is difficult to translate into an ASIC/FPGA world, it’s the concept of user story. Perhaps it’s because I simply don’t have the experience in writing user stories. But I think it has more to do with my trouble in writing an ASIC story from a user’s perspective. In many cases, a feature does not even provide any meaningful output that is visible to the user e.g., some esoteric standards requirement about how an interface must be defined.
Then serendipity came through for me, when my former colleague and AgileSoC collaborator Neil Johnson was in town on vacation and wanted to grab a beer. He knew James Grenning , who happened to be in Ottawa at the same time to deliver some training, and invited him along too. I’ll cut it short by saying I had a very intersting conversation with James and Neil. You see James is an expert in Test Driven Development for embedded systems. In fact, he’s written a book on the topic Test Driven Development for Embedded C. It was very interesting to discover the similarities that exist between embedded system design and SoC development. Including the perceived and real barriers to adopting an agile flow in an embedded design.
To cut to the chase, we got to talking about user stories and how they don’t really fit into the ASIC development, when James suggested that he calls user stories “Product Stories” instead. While its a simple semantic change of “user” to “product”, for me it was a lightbulb moment. It helped me identify the issue I’ve been having with ‘user stories’: I’m not implementing something for an end-user; I’m developing a product that will fit into a larger system that will ulimately be seen by a user.
Like User Stories, Product Stories are intended to be very high level descriptions of the features that you want to develop along with the acceptance testing that proves the feature is what you expect. The key is that these are short descriptions from the system’s perspective. Instead of the who, what and why as in a user story the product story for ASIC development should include the where,what and why. Specifically, a good requirement contains the following elements:
Behaviour: (the what) A short descriptive story explaining the behaviour at a high level. Justification: (the why) Some idea on why this is important to the system (unless it’s absolutely clear e.g., some standard protocol); Context: (the where) Where in the system this feature is needed Acceptance: simple set of acceptance tests to prove that behaviour is correct.
I’ve been developing the following template, that I’ll be considering to use for my Product Stories, which is similar to the ‘user story’ template above.
“The <context> needs to <do some behaviour> so that <some reason> “.
A product story provides some clear guidelines on the functionality expected, as well as a clear indication of what coverage points must be captured before you declare the product story complete. In fact, I think it might be a good idea to stating these acceptance criteria as functional coverage points.
As I work through these concepts in my head, I’ll attempt to describe them in in my next few blog posts. I’ll talk about how I see these Product Stories being created, developed and tracked in an AgileSoC world.
I’d welcome any comments on this post, and especially how you are doing your requirements management – especially when requirements are very fluid (which, I’m guessing, is probably most of the time for most of us ).