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5 Requirements Analysis

This section specifies the user and system requirements for an interactive computer simulation of visual impairments.

5.1 Method

Contextual Enquiry is a method used for requirements gathering that is based on observing and interviewing users to explore the nature of their work [34]. This method could have been adapted to interview people with visual impairments to determine the requirements for a computer simulation. However there are a large number of visual impairments, each of which affects different people in different ways and at different severities. Extracting the requirements for a simulation of visual impairments in this way would have been a lengthy process. Instead the requirements were based on the symptoms described in Section 2 and existing simulations of visual impairments as shown in Appendix A.

5.2 Functional Requirements

The functional requirements are described by Sommerville [32] as "statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations." The functional requirements for the simulation are outlined below:

Req 1.  The software shall simulate the symptoms of one or more visual impairments
Req 1.1  The software should simulate myopia.
Req 1.2  The software should simulate hyperopia.
Req 1.3  The software should simulate glaucoma.
Req 1.4 The software should simulate retinitis pigmentosa.
Req 1.5  The software should simulate macular degeneration.
Req 1.6 The software should simulate diabetic retinopathy.
Req 1.7  The software should simulate hemianopia.
Req 1.8  The software should simulate cataracts.
Req 1.9  The software should simulate colour blindness.
Req 2.  The software simulation shall be dynamic
Req 2.1  The software should simulate the movement of the field of vision.
Req 2.2  The software should simulate varying the focal length of the vision.
Req 3.  The user shall be able to interact with the simulation.
Req 3.1  The user should be able to change the type of impairment.
Req 3.2  The user should be able to adjust the severity of the impairment.
Req 3.3  The user should be able to select the centre of the field of vision.
Req 3.4  The user should be able to change the focal length of the vision.
Req 3.5  The user should be able to save and recall default settings for the type and severity of the impairment and the position of the centre of the field of vision.
Req 3.6  The user should be able to exit the simulation.
Req 4.  The simulation shall run in true full screen mode
Req 4.1  The simulation should use a window that has no title bar or borders and has the dimensions of the screen.
Req 5.  The software shall simulate the use of a computer with a visual impairment
Req 5.1  The simulated impairments should be applied to the displayed output of other software applications.
Req 5.2  The user should be able to interact with other software applications in the normal manner by using the mouse and keyboard or other input devices.

These requirements are discussed in Sections 6.1 to 6.5.

5.3 Non-functional requirements

The non-functional requirements are described by Sommerville [32] as "constraints on the services or functions offered by the system." The non-functional requirements for the simulation are outlined below. The usability requirements were based on Nielsen's Usability Heuristics which are "general principles for user interface design" [35].

Req 6.  Usability Requirements
Req 6.1  The system should be consistent.
Req 6.2  The system should provide appropriate feedback.
Req 6.3  The system should allow easy reversal of actions.
Req 6.4  The system should provide shortcuts.
Req 6.5  The system should allow customisation of actions.
Req 6.6  The system should provide help and documentation.
Req 7.  Performance Requirements
Req 7.1  It should take no longer than 30 seconds to start the system.
Req 7.2  It should take no longer than 10 seconds for a setting change to take effect.

5.4 Summary

The functional requirements for a simulation of visual impairments were gathered from the analysis of existing simulations and descriptions of the symptoms of visual impairments. Usability requirements for the system were based on Nielsen's Usability Heuristics [35]. Performance requirements for the system were also specified.


Stephen Ratcliffe. 2005
Department of Computer Science
University of York
Heslington
York
YO10 5DD