Sommerville-Software-Engineering-10ed

428 Chapter 14 ■ Resilience engineering
Mentcare
client
Mentcare
client
Mentcare
client
Network
Mentcare server
Figure 14.10 The
client–server architecture
of the Mentcare system
Patient database
Testing can be very difficult and expensive as, obviously, the testing cannot be carried
out on an operational system. The system and its environment may have to be duplicated
for testing, and staff may have to be released from their normal responsibilities to work
on the test system. To reduce costs, you can use “desk testing.” The testing team assumes
a problem has occurred and tests their reactions to it; they do not simulate that problem
on a real system. While this approach can provide useful information about system resilience,
it is less effective than testing in discovering deficiencies in the resilience plan.
As an example of this approach, let us look at resilience engineering for the
Mentcare system. To recap, this system is used to support clinicians treating patients
in a variety of locations who have mental health problems. It provides patient information
and records of consultations with doctors and specialist nurses. It includes a
number of checks that can flag patients who may be potentially dangerous or suicidal.
Figure 14.10 shows the architecture of this system.
The system is consulted by doctors and nurses before and during a consultation,
and patient information is updated after the consultation. To ensure the effectiveness
of clinics, the business resilience requirements are that the critical system services
are available during normal working hours, that the patient data should not be permanently
damaged or lost by a system failure or cyberattack, and that patient information
should not be released to unauthorized people.
Two critical services in the system have to be maintained:
1. An information service that provides information about a patient’s current diagnosis
and treatment plan.
2. A warning service that highlights patients who could pose a danger to others or
to themselves.
Notice that the critical service is not the availability of the complete patient
record. Doctors and nurses only need to go back to previous treatments occasionally,