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Approaches to software development
Approaches to software development

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System boundaries

The system boundary is a conceptual line that divides the system that you want to study from ‘everything else’. It is useful to think of a system’s environment as being made up of those things that are not part of the system, but can either affect the system or be affected by it. Example 4 takes you into a particular area of interest, which is known as a domain, to look at system boundaries and how they can change.

Example 4

A hospital is a domain where software is put to a variety of uses. A hospital might, for example, join together a series of patient-monitoring systems with the database management system that manages medical records, creating a larger system with a different scope. A forward-looking hospital might wish to go further and add weather-forecasting software. This extension would allow planners to deal with the variations in flow of patients that arise according to the season. Beds may be allocated and other resources, such as drugs, bought in preparation.

Activity 1 Combining systems

Timing: Allow approximately 10 minutes.

In Example 4, we suggested that two systems, for patient monitoring and managing medical records, might be combined into a single system. Suggest an additional function that might be possible with the combined system that would not have been possible with either of the two original systems alone. What can you say about the boundary of the combined system compared with the boundaries of the original separate systems?


Suppose the monitoring system detected that a patient taking a common drug had a heart problem. If the two systems were combined, it would be possible to automatically check whether the heart problem might be due to a known allergy recorded in the patient’s record.

The boundary of the combined system encompasses a wider scope than the combined boundaries of the separate systems because the combination of patient monitoring and medical records supports a wider range of verifications.