Answer to Question #316720 in Computer Networks for Yanda

Question

Discuss the ways in which a full-page word processor is or is not a direct manipulation interface for editing a document using Schneider man's criteria. What features of a modern word processor break the metaphor of composition with pen (or typewriter) and paper?

(15)marks

Answer 1

We will answer the first question by evaluating the word-processors relative to the criteria for direct manipulation given by Shneiderman.

Visibility of the objects of interest: The most important objects of interest in a word-processor are the words themselves. Indeed, the visibility of the text on a continual basis was one of the major usability advances in moving from line-oriented to display-oriented editors. Depending on the users application, there may be other objects of interest in word-processing that may or may not be visible. For example, are the margins for the text on screen similar to the ones which would eventually printed? Is the spacing within a line and the line-breaks similar? Are the different fonts and formatting characteristics of the text visible (without altering the spacing)? Expressed in this way, we can see the visibility criterion for direct manipulation as very similar to the criteria for a WYSIWYG (What You See Is What You Get) interface.

Incremental action at the interface with rapid feedback on all actions: We expect from a modern word-processor that characters appear in the text as we type them it at the keyboard, with little delay. If we are inserting text within a paragraph, we might also expect that the format of the paragraph adjust immediately to accommodate the new changes. Various word processors do this reformatting automatically, whereas others do it occasionally or only at the explicit request of the user. One of the other important actions which require incremental and rapid feedback is movement of the insertion point, usually by means of arrow keys. If there is a significant delay between the input command to move the insertion point down one line and the actual movement of the cursor on screen, it is quite possible that the user will overshoot the target when repeatedly pressing the down-arrow key to move down a few lines on the screen.

Reversibility of all actions, so that users are encouraged to explore without severe penalties: Single step undo commands in most word-processors allow the user to recover from the last action performed. One problem with this is that the user must recognize the error before doing any other action. More sophisticated undo facilities allow the user to retrace back more than one command at a time. The kind of exploration this reversibility provides in a word-processor is best evidenced with the ease of experimentation that is now available for June 4, 1993 17:34 exercises Sheet number 28 Page number 26

26 Usability Paradigms and Principles formatting changes in a document (fonts types and sizes and margin changes). One problem with the ease of exploration is that emphasis may move to the look of a document rather than what the text actually says (style over content).

Syntactic correctness of all actions, so that every operation is a legal operation WYSYWYG: word-processors usually provide menus and buttons which the user uses to articulate many commands. These interaction mechanisms serve to constrain the input language to only allow legal input from the user. Document production systems, such as troff, TeX, and Scribe, force the user to input textual commands (which may be erroneously entered by the user) to achieve desired formatting effects.