Cognition: Mental Representations, Problem Solving, and Decision Making - Foundations for Designing User-Centered Systems - page 172

an accurate view of the actual starting state (you may have an old version installed)
and you might not know the actual constraints on the installation process (e.g., you
cannot install a new version correctly if the old version is still on the computer).
Software can help with this, for example, noting the constraints for you.
In many hardware configurations for PCs there are hidden constraints: some
disks require particular drives and graphics cards may require specific pieces of
software as well. These constraints are often hidden, and sometimes can only be
found through applying expensive operators, that is, configuring the hardware and
then testing.
Problem solving is effortful and time consuming. In aviation they try to min-
imize the amount of problem solving that flight crews have to perform by pro-
viding a Quick Reference Handbook (QRH). This is essentially a set of procedures
(checklists) that can be used to deal with known situations, both common and rare.
In this way the pilots can operate at Rasmussen's rule-based level. In extreme
situations, however, they may have to resort to problem solving. In the Sioux City
air accident (NTSB 1990 ), for example, the aircraft lost all of its hydraulics
systems whilst in the air, which basically meant that it could not be steered in the
normal manner. The likelihood of such an event was so remote that there was no
procedure to deal with it in the QRH, and even the aircraft manufacturer did not
have a way to steer the aircraft. Fortunately there was another pilot on the aircraft
who, together with the flight crew, worked out a way to steer the aircraft and get it
down onto the ground.
6.3.3 Known Influences on Problem Solving
There are several known effects and influences on problem solving. These include
ways that people like to problem solve and known ways that they are inefficient at
problem solving. Knowing these effects can help build better interfaces and
systems.
6.3.3.1 Based on Mental Models
Problem solving and decision making are thoroughly rooted in our world
knowledge and world experiences. In trying to understand unfamiliar machines or
unfamiliar behavior of common machines we try to construct a mental model
(imagined world) in which we understand the device. This model enables us to
operate the machine without having to recall what to do from memory. The
correspondence between the imagined world and the real world is not important as
long as the operations make sense in the imagined world, our mental model.
Mental models are thus used to perform Means-Ends Analysis (MEA) when
problem solving. This approach to problem solving examines the current state of
the device and notices differences between it and the solution. Systems that