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Sometimes a realistic problem seems to have an easily
identified core that fits a recognised problem. You
can start by taking the core first and working outwards.
We decided easily, at the outset, the the core Package Router problem was a required behaviour control problem
There are usually sub problems surrounding the core
(typically information subproblems). Info subproblems
usually easy to separate out from the core; it treats
its real world as autonomous
Some problem frames are composites and have standard
decompositions. When we recognised the information
display problem we saw it would require a dynamic
model and also needed a static model.
Concerns and difficulties
Examine sub problem for common or characteristic concerns and
difficulties – often they will reveal further sub
Session of tennis takes an hour or two; a member’s
subscription is valid for a season or for a year, or
even longer. This shows there are at least two different sub problems here.
Managing subscriptions is a dynamic domain: members join and
leave, pay or don’t pay subscriptions.
Managing court and its lights: treat membership as
Billing for lights is a third subproblem because it straddles
two tempi. Items to be billed are games of tennis,
recorded in the fast problem. Billing and payment
proceeds at a slower pace, perhaps monthly. Late payers and defaulters may find their membership suspended.
An assertion of fact. If the motor polarity is set to up and the motor switch setting is changed from off to on the lift starts to rise within 250 msecs (properties
of the motor and winding gear).
Expresses a wish. If an up call button is pressed when the
corresponding light is off the light comes on and
remains on until the call is serviced by the lift stopping
at that floor and leaving in the upwards direction.
Subproblem 1: based on (a) and (b). (a) is given and the
requirement is (b)
Subproblem 2: detect failures to satisfy (b)
Subproblem 3: based on (a) the negation of (b) and on (c):
(a) is given, NOT (b) is given, and the requirement is
A is indicative – what’s true anyway
B is optative – what customer ideally wants
C is super-optative – what customer must have if B is