This guide to getting started with the Spiral Development Model is a very condensed summary of Boehm et al.. For more details, check out the original whitepaper here.
Your first major objective is to get to the Life-Cycle Objectives (LCO) Milestone and show that there exists a viable (business) case for at least one system proposal. In the first cycle you will likely only do the key activities outlined in Invariant A, with the goal of creating initial versions of the key artifacts. Later iterations will include development and planning phases. For each cycle, you will need to go through the key phases and have stakeholders willing to do a review, the focus thereof being the key artifacts and the feasibility rationale (see Invariant E). If helpful, you can also do mini-cycles (i.e. for a prototype). The Invariants of the Spiral Model are: Continue reading The Spiral Development Model — Getting Started→
After what has been a very long pause, we’re going to go in a bit of a different direction and take a look at some project management, specifically the Spiral Development Model, which is software development process model. It can also be used for other development processes though. Like all process models, it tries to answer a few central questions:
What should we do next?
How long should we continue?
What can we do to have a high chance of completing our project successfully?
It’s a bit of a long post, but I think weighted-sums as a decision making tool is awesome! I would whole-heartedly recommend it to anyone who’s has to make a complicated decision.
With so many options at hand which more or less matched the design brief, and so many factors to consider, I was going to need a structured approach to have any chance of arriving at a conclusive decision. My dad lent me a book “Contemporary Management Science with Spreadsheets“, and recommended that I read the chapter on multi-criteria decision-making. Being in a bit of a state of despair, but determined to resolve the issue, I flipped open the book and started reading. The chapter featured two techniques, weighted sums and the more complex analytic hierarchy process, which relies on a very large number of pairwise decisions. I chose weighted sums because it’s the simpler method of the two.
Method – Weighted Sums
Pick out clear candidates (decision alternatives) for the process
Decide which criteria are relevant for your decision
Give each criterion a relative weight, for how important it is to you
For each candidate, rate how well it satisfies each of the criteria
Calculate rating x weight for each entry, and then add those up for a total score for each candidate
When I started my quest to find the right design over Christmas, I had a few things going for me: I had a clear design brief, I’d also spent a good deal of time looking into the possibility of building a somewhat smaller trimaran in the weeks before, and had done some rough calculations showing that a tacking outrigger, even if it’s only 7m long, is actually viable option. The solution space is enormous though. Overall I considered everything ranging from modular hulls, to smaller proas, tacking proas, a small trimaran such Newick’s Tremolino design (where you take the rig and floats of a large beachcat and build a central hull yourself), an i550 (a small and very neat monohull sportsboat), to even a simple open sailing & rowing dory or perhaps something like a Goat Island Skiff.