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User Interface Design and Ergonomics - National Open University of ...

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affect the way the comm<strong>and</strong> is executed. The following screen dump shows a comm<strong>and</strong><br />

prompt - in this case, the user has logged on to a (mail) server <strong>and</strong> can use the server's<br />

functions by typing in comm<strong>and</strong>s.<br />

Figure 5: Comm<strong>and</strong> prompt. The comm<strong>and</strong> "ls- al" has just been executed<br />

('ls' st<strong>and</strong>s for 'list' <strong>and</strong> the parameters '-al' specify that the list comm<strong>and</strong> should display a<br />

detailed list <strong>of</strong> files).<br />

Comm<strong>and</strong> language places a considerable cognitive burden on the user in that the<br />

interaction style relies on recall as opposed to recognition memory. Comm<strong>and</strong>s as well as<br />

their many parameterised options have to be learned by heart <strong>and</strong> the user is given no<br />

help in this task <strong>of</strong> retrieving comm<strong>and</strong> names from memory. This task is not made easier<br />

by the fact that many comm<strong>and</strong>s (like the 'ls' comm<strong>and</strong> in the above example) are<br />

abbreviated in order to minimize the number <strong>of</strong> necessary keystrokes when typing<br />

comm<strong>and</strong>s. The learnability <strong>of</strong> comm<strong>and</strong> languages is generally very poor.<br />

Advantages <strong>of</strong> Comm<strong>and</strong> Language<br />

Flexible.<br />

Appeals to expert users.<br />

Supports creation <strong>of</strong> user-defined "scripts" or macros.<br />

Is suitable for interacting with networked computers even with low b<strong>and</strong>width.<br />

Disadvantages<br />

Retention <strong>of</strong> comm<strong>and</strong>s is generally very poor.<br />

Learnability <strong>of</strong> comm<strong>and</strong>s is very poor.<br />

Error rates are high.<br />

100

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