HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
5.1 Can you think of any instances in which the 'noun-- verb' guideline for operations, as suggested in the Apple human interface guidelines for the Desktop
This chapter and the next three describe a range of models that can be used during the interface design process. Just as in the design of the office block several different types of model are required for different aspects of the building, so in interface design we would expect to use a whole selection of complementary methods.
The remaining techniques and models in this chapter all claim to have some representation of users as they interact with an interface; that is, they model some aspect of the user's understanding, knowledge, intentions or processing. The level of representation differs from technique to technique -- from models of high-level goals and the results of problem-solving activities, to descriptions of motor-level activity, such as keystrokes and mouse clicks. The formalisms have largely been developed by psychologists, or computer scientists whose interest is in understanding user behaviour.
We have seen how CCT rules may be informally analyzed to discuss issues of proceduralization and error behaviour, and how we can relate them to GOMS-like goal hierarchies. However, the main aim of CCT is (as its name suggests) to be able to measure the complexity of an interface.
Basically, the more production rules in the CCT description the more difficult the interface is to learn. This claim rests on the assumption that the production rules represent reasonably accurately the way knowledge is stored and therefore that the time taken to learn an interface is roughly proportional to the number of rules you have to learn.
There are various problems with CCT. As with many 'rich' description methods, the size of description for even a part of an interface can be enormous. Furthermore, there may be several ways of representing the same user behaviour and interface behaviour, yielding different measures of dissonance. To some extent this is catered for by the novice style rules, but there is no such set of rules for the system description.
On the positive side, the conceptual framework of goal hierarchies and user goal stacks can be used to express interface issues, not directly addressed by the notations above. For instance, early automated teller machines gave the customers the money before returning their cards. Unfortunately, this led to many customers leaving their cards behind. This was despite on-screen messages telling them to wait. This is referred to as a problem of closure. The user's principal goal is to get money; when that goal is satisfied, the user does not complete or close the various subtasks which still remain open:
The user's interaction with a computer is often viewed in terms of a language, so it is not surprising that several modelling formalisms have developed centred around this concept. Several of the dialog notations described in Chapter 8 are also based on linguistic ideas. Indeed, BNF grammars are frequently used to specify dialogs. The models here, although similar in form to dialog design notations, have been proposed with the intention of understanding the user's behaviour and analyzing the cognitive difficulty of the interface.
The BNF description of an interface can be analyzed in various ways. One measure is to count the number of rules. The more rules an interface requires to use it, the more complicated it is. This measure is rather sensitive to the exact way the interface is described. For example, we could have replaced the rules for choose-points and choose-one with the single definition
choose-points ::= position-mouse + CLICK-MOUSE
| position-mouse + CLICK-MOUSE + choose-points
processed in 0.006 seconds
|
| |
|
HCI Book 3rd Edition || old HCI 2e home page || search
|
|
| feedback to feedback@hcibook.com | hosted by hiraeth mixed media |
|
| |