HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
More and more computer users are becoming familiar with interaction based on windows, icons, menus and pointers -- the WIMP interface. These interaction devices first appeared in the commercial marketplace in April, 1981, when Xerox Corporation introduced the 8010 Star Information System. But many of the interaction techniques underlying a windowing system were used in Engelbart's group in NLS and at Xerox PARC in the experimental precursor to Star, the Alto.
In the early 1980s as the price of fast and high-quality graphics hardware was steadily decreasing, designers were beginning to see that their products were gaining popularity as their visual content increased. As long as the user--system dialog remained largely unidirectional -- from user command to system command line prompt -- computing was going to stay within the minority population of the hackers who revelled in the challenge of complexity. In a standard command line interface, the only way to get any feedback on the results of previous interaction is to know that you have to ask for it and to know how to ask for it. In terms of the interaction framework discussed in Chapter 3, not every articulated input expression from the user is accompanied by some output expression which reveals an underlying change in the internal state of the system. Rapid visual and audio feedback on a high-resolution display screen or through a high-quality sound system makes it possible to provide evaluative information for every executed user action.
Rapid feedback is just one feature of the interaction technique known as direct manipulation. Ben Shneiderman [218, 219] is attributed with coining this phrase in 1982 to describe the appeal of graphics-based interactive systems such as Sketchpad and the Xerox Alto and Star. He highlights the following features of a direct manipulation interface:
The first real commercial success which demonstrated the inherent usability of direct manipulation interfaces for the general public was the Macintosh personal computer, introduced by Apple Computer, Inc. in 1984 after the relatively unsuccessful marketing attempt in the business community of the similar but more pricey Lisa computer. We discussed earlier how the desktop metaphor makes the computer domain of file management, usually described in terms of files and directories, easier to grasp by likening it to filing in the typical office environment, usually described in terms of documents and folders. The direct manipulation interface for the desktop metaphor requires that the documents and folders are made visible to
In a system built on the model-world metaphor, the interface is itself a world where the user can act, and which changes state in response to user actions. The world of interest is explicitly represented and there is no intermediary between user and world. Appropriate use of the model-world metaphor can create the sensation in the user of acting upon the objects of the task domain themselves. We call this aspect of directness direct engagement.
In the model-world metaphor, the role of the interface is not so much one of mediating between the user and the underlying system. From the user's perspective, the interface is the system.
Somewhat related to the visualization provided by direct manipulation is the WYSIWYG paradigm, which stands for 'What you see is what you get'. What you see on a display screen, for example when you are using a word processor, is not the actual document that you will be producing in the end. Rather, it is a representation or rendering of what that final document will look like. The implication with a WYSIWYG interface is that the difference between the representation and the final product is minimal, and the user is easily able to visualize the final product from the
With WYSIWYG interfaces, it is the simplicity and immediacy of the mapping between representation and final product that matters. In terms of the interaction framework, the observation of an output expression is made simple so that assessment of goal achievement is straightforward. But WYSIWYG is not a panacea for usability. What you see is all you get! In the case of a word processor, it is difficult to achieve more sophisticated page design if you must always see the results of the layout on screen. For example, suppose you want to include a picture in a document you are writing. You design the picture and then place it in the current draft of your document, positioning it at the top of the page on which it is first referenced. As you make changes to the paper, the position of the picture will change. If you still want it to appear at the top of a page, you will no doubt have to make adjustments to the document. It would be easier if you only had to include the picture once, with a directive that it should be positioned at the top of the printed page, whether or not it appears that way on screen. You might sacrifice the WYSIWYG principle in order to make it easier to incorporate such floatable objects in your documents.
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