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Defined Selection

Problem

The user need to select data from a well-know closed set.

The main characteristic of this type of selection is that the selection set is totally determined at analysis time. The analyst is able to describe all the elements that conform the selection set by enumeration.

Defined Selection Sample 1
Figure 1. Sample controls in Windows
for implementing Defined Selection.

Principle

Guiding, Error prevention.

Forces

Solution

The system should show to the user a set of options or values. The user will pick one (single selection) or more that one (multiple selection).

The system helps to prevent errors impeding the selection of non correct values.

Rationale

Make evident all the choices to the user. Constrains the values down to the possible ones.

Examples

Radiobuttons, combo-boxes, list, & drop-down controls are good examples of controls used in Windows (Figure 1) to implement this type of selection.

Specification

The selection set can be defined by extension, providing a enumeration of the values defines.

Its also important to separate the visible label for the user, respect to the code used internally by the system. This distinction will allow later maintenance UI changes without affecting the application's logic and vice versa. E.g. consider applying localization patterns to the User Interface.






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