HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
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.
Whereas it is true that direct manipulation interfaces make some tasks easier to perform correctly, it is equally true that some tasks are more difficult, if not impossible. Contrary to popular wisdom, it is not generally true that actions speak louder than words. The image we projected for direct manipulation was of the interface as a replacement of the underlying system as the world of interest to the user. Actions performed at the interface replace any need to understand their meaning at any deeper, system level. Another image is of the interface as the interlocutor or mediator between the user and the system. The user gives the interface instructions and it is then the responsibility of the interface to see that those instructions are carried out. The user--system communication is by means of indirect language instead of direct actions.
As another example of the benefit of immediate over eventual honesty, let us examine a typical global search and replace function in a word processor. Imagine you have noticed in the past a tendency to repeat words in a document (for example, you type 'the the' without noticing the error). In an attempt to automate your proof-reading, you decide to replace globally all occurrences of 'the the' with 'the'. The typical global search and replace function performs this substitution without revealing the changes made to you. Suddenly, a careless typing error is transformed into unacceptable grammar as the sentence
New users of a system bring with them a wealth of experience across a wide number of application domains. This experience is obtained both through interaction in the real world and also through interaction with other computer systems. For a new user, the familiarity of an interactive system measures the correlation between the user's existing knowledge and the knowledge required for effective interaction. For example, when word processors were originally introduced, the analogy between
Consistency can be expressed in terms of the form of input expressions or output responses with respect to the meaning of actions in some conceptual model of the system. For example, before the introduction of explicit arrow keys, some word processors used the relative position of keys on the keyboard to indicate directionality for operations (for example, to move one character to the left, right, up or down). The conceptual model for display-based editing is a two-dimensional plane, so the user would think of certain classes of operations in terms of movements up, down, left or right in the plane of the display. Operations which required directional information, such as moving within the text or deleting some unit of text, could be articulated by using some set of keys on the keyboard which form a pattern consistent with up, down, left and right (for example, the keys e, x, s and d, respectively). For output responses, a good example of consistency can be found in a warnings system for an aircraft. Warnings to the pilot are classified into three categories, depending on whether the situation with the aircraft requires immediate recovery action, eventual but not immediate action, or no action at all (advisory) on the part of the crew. These warnings are signalled to the crew by means of a centralized warnings panel in which the categories are consistently colour coded (red for immediate, amber for eventual and green for advisory).
Spell-checking a paper is a good example of the need for task migratability. Equipped with a dictionary, you are perfectly able to check your spelling by reading through the entire paper and correcting mistakes as you spot them. This mundane task is perfectly suited to automation, as the computer can check words against its own list of acceptable spellings. It is not desirable, however, to leave this task completely to the discretion of the computer, as most computerized dictionaries do not handle proper names correctly, nor can they distinguish between correct and unintentional duplications of words. In those cases, the task is handed over to the user. The spell-check is best performed in such a cooperative way.
Discuss the ways in which a full-page word processor is or is not a direct manipulation interface for editing a document using Shneiderman's criteria. What features of a modern word processor break the metaphor of composition with pen (or typewriter) and paper?
We will answer the first question by evaluating the word processors relative to the criteria for direct manipulation given by Shneiderman.
processed in 0.008 seconds
|
| |
|
HCI Book 3rd Edition || old HCI 2e home page || search
|
|
| feedback to feedback@hcibook.com | hosted by hiraeth mixed media |
|
| |