Continuous characteristics can take any value over a certain range. Thus, fuel
consumption can vary between 5 and 25 litres per 100 km, while the time taken to
accelerate from 0 km to 100 km per hour may vary between 8 and 20 s. These
continuous variables are called objective because the values can be accurately
established by independent measurement and are not dependent on the opinion of
any individual customer. Continuous characteristics are also referred to as variables.
Discrete characteristics are usually used for assessing less tangible features.
Examples would include the visual appeal of a chair or a sofa, its comfort, the inside
of an office. Only four to six discrete values are normally allocated to such a
characteristic. Thus, the visual appeal of the chair could be assessed using the five
to seven numbers 1 to 5 or 1 to 7, distributed as follows: 6 (Excellent), 5 (Very Good)
4 (Good), 3 (Average), 2 (Poor), I (Very Poor) or in inverse order. This is also called
the Likert scale. These discrete characteristics are also subjective, that is, dependent
on the opinion of an individual customer. However, one customer may regard a
given body style as excellent, whereas another may judge it to be merely average.
Binary characteristics distinguish features that can only have two states: Yes
or No: the good possesses the feature or not, the infrastructure either passes the test
or fails it. Very often the results may be expressed using only two values (binary):
0 or 1 corresponding to present/not present or pass/fail. Examples are ability/
inability for a laptop to run more than 4 h on batteries, ability/inability for a generator
to supply electricity in less than 15 s after start, ability/inability for the transport
system to follow a time schedule. Binary characteristics are also called attributes.
Figure 9.1 shows a typical arrangement where water is pumped from a borehole
into a ground reservoir, from where it is further pumped (boosted) into a service
reservoir, before being distributed to houses and other consumers. Table 9.2 gives
features which would characterize the performance of the pumps, and the pump
room and classify the arrangement as belonging to the “satisfactory, good, or high”
quality class.
To sum up, the quality of an infrastructure service (engineering product) can be
specified by three sets of output performance characteristics (Fig. 9.2). The set of
numbers Xl, X2,. . ., i.e. the vector {x}, specifies the continuous characteristics; the
Town
Service Reservoir
Submersible
Pump P 1
Ground
Reservoir
Booster
Pump P 2
X
Y
Houses receive water at a pressure of Z metres of water.
Water is pumped (P1) from borehole from a depth of X metres.
A booster pump (P2) sends water to a service reservoir Y metres,
above borehole ground level.
QUESTION: How to ensure that the houses always receive water?
Z
Fig. 9.1 Typical distribution system from a borehole
256
9 Quality and Reliability of Infrastructure
consumption can vary between 5 and 25 litres per 100 km, while the time taken to
accelerate from 0 km to 100 km per hour may vary between 8 and 20 s. These
continuous variables are called objective because the values can be accurately
established by independent measurement and are not dependent on the opinion of
any individual customer. Continuous characteristics are also referred to as variables.
Discrete characteristics are usually used for assessing less tangible features.
Examples would include the visual appeal of a chair or a sofa, its comfort, the inside
of an office. Only four to six discrete values are normally allocated to such a
characteristic. Thus, the visual appeal of the chair could be assessed using the five
to seven numbers 1 to 5 or 1 to 7, distributed as follows: 6 (Excellent), 5 (Very Good)
4 (Good), 3 (Average), 2 (Poor), I (Very Poor) or in inverse order. This is also called
the Likert scale. These discrete characteristics are also subjective, that is, dependent
on the opinion of an individual customer. However, one customer may regard a
given body style as excellent, whereas another may judge it to be merely average.
Binary characteristics distinguish features that can only have two states: Yes
or No: the good possesses the feature or not, the infrastructure either passes the test
or fails it. Very often the results may be expressed using only two values (binary):
0 or 1 corresponding to present/not present or pass/fail. Examples are ability/
inability for a laptop to run more than 4 h on batteries, ability/inability for a generator
to supply electricity in less than 15 s after start, ability/inability for the transport
system to follow a time schedule. Binary characteristics are also called attributes.
Figure 9.1 shows a typical arrangement where water is pumped from a borehole
into a ground reservoir, from where it is further pumped (boosted) into a service
reservoir, before being distributed to houses and other consumers. Table 9.2 gives
features which would characterize the performance of the pumps, and the pump
room and classify the arrangement as belonging to the “satisfactory, good, or high”
quality class.
To sum up, the quality of an infrastructure service (engineering product) can be
specified by three sets of output performance characteristics (Fig. 9.2). The set of
numbers Xl, X2,. . ., i.e. the vector {x}, specifies the continuous characteristics; the
Town
Service Reservoir
Submersible
Pump P 1
Ground
Reservoir
Booster
Pump P 2
X
Y
Houses receive water at a pressure of Z metres of water.
Water is pumped (P1) from borehole from a depth of X metres.
A booster pump (P2) sends water to a service reservoir Y metres,
above borehole ground level.
QUESTION: How to ensure that the houses always receive water?
Z
Fig. 9.1 Typical distribution system from a borehole
256
9 Quality and Reliability of Infrastructure