Civil Engineering Reference
In-Depth Information
TABLE 15.5
Representation of a Nuclear Power
Plant in Terms of Means-Ends and Whole-Part
Decomposition
Abstraction
Level
Means-Ends
Whole-Part
1
Purpose
Functional purposes and goals in terms of energy,
material flow, and distribution
Why
2
Abstract
function
Mass, energy flow, and balance in terms of
underlying generic functions
What, Why
3
Generalized
function
Info on cooling, heat transfer, regulation in terms
of connected pieces of equipment
How, What,
Why
4
Physical
function
Performance data on physical equipment in terms
of information on components
How, What
5
Physical form
Installation and maintenance info on components:
take-apart diagrams, illustrations
How
Adapted from Konz (1990). The lower the learning rate, the greater the improvement in
performance time.
TABLE 15.6
Abstraction Levels and Means-
Ends Decomposition for Water Pump
Abstraction Level
Means-Ends
1. Purpose Supply water Why
2. Abstract function Pump water What, Why
3. Generalized function Use human-machine system How, What, Why
4. Physical function
Use bellows
How, What
5. Physical form
Use mechanical movements
How
Another example is illustrated in Table 15.6 and Figure 15.6. This is a depiction of
Vittorio Zonca's engraving of a bellows pump from 1607 (Helander, 1996). This system
can be broken down into five abstraction levels, from the top purpose or goal of the
system to the bottom, which illustrates design details. Let's say you are at the second
level of abstraction, “Pump Water,” and you ask yourself why. This question brings you
to the first abstraction level, “Supply Water.”
Rasmussen claimed that the analytical approach of a system is useful in order to
analyze several usability questions, including the following:
• Determine the functionality of the device
• Tell what actions are possible
• Tell what state the system is in
• Determine mapping from intention to physical movement
• Determine mapping from system state to interpretation
One example is the analysis of the work of a maintenance technician that is illustrated in
Figure 15.7 (Rasmussen, 1990). In this case there is a division according to abstraction
level as well as systems level. The reason for the maintenance action is stated at number
