Archives For Assumptions

Technical debt

05/09/2015 — 1 Comment

St Briavels Castle Debtors Prison (Image source: Public domain)

Paying down the debt

A great term that I’ve just come across, technical debt is a metaphor coined by Ward Cunningham to reflect on how a decision to act expediently for an immediate reason may have longer term consequences. This is a classic problem during design and development where we have to balance various ‘quality’ factors against cost and schedule. The point of the metaphor is that this debt doesn’t go away, the interest on that sloppy or expedient design solution keeps on getting paid every time you make a change and find that it’s harder than it should be. Turning around and ‘fixing’ the design in effect pays back the principal that you originally incurred. Failing to pay off the principal? Well such tales can end darkly. Continue Reading…

Toyota ECM (Image source: Barr testimony presentation)

Comparing and contrasting

In 2010 NASA was called in by the National Highway Transport Safety Administration to help in figuring out the reason for reported unintended Toyota Camry accelerations. They subsequently published a report including a dedicated software annex. What’s interesting to me is the different outcome and conclusions of the two reports regarding software.  Continue Reading…

Process is no substitute for paying attention

As Weick has pointed out, to manage the unexpected we need to be reliably mindful, not reliably mindless. Obvious as that truism may be, those who invest heavily in plans, procedures, process and policy also end up perpetuating and reinforcing a whole raft of expectations, and thus investing in an organisational culture of mindlessness rather than mindfulness.

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An articulated guess beats an unspoken assumption

Frederick Brooks

A point that Fred Brooks makes in his recent work the Design of Design is that it’s wiser to explicitly make specific assumptions, even if that entails guessing the values, rather than leave the assumption un-stated and vague because ‘we just don’t know’. Brooks notes that while specific and explicit assumptions may be questioned, implicit and vague ones definitely won’t be. If a critical aspect of your design rests upon such fuzzy unarticulated assumptions, then the results can be dire.

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Did the designers of the japanese seawalls consider all the factors?

In an eerie parallel with the Blayais nuclear power plant flooding incident it appears that the designers of tsunami protection for the Japanese coastal cities and infrastructure hit by the 2011 earthquake did not consider all the combinations of environmental factors that go to set the height of a tsunami.

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Thinking about the unintentional and contra-indicating stall warning signal of AF 447 I was struck by the common themes between AF 447 and the Titanic. In both the design teams designed a vehicle compliant to the regulations of the day. But in both cases an implicit design assumption as to how the system would be operated was invalidated.

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Blayais Plant (Image source: Wikipedia Commons)

What a near miss flooding incident at a French nuclear plant in 1999 and the Fukushima 2012 disaster can tell us about fault tolerance and designing for reactor safety

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