Introduction to Graphical Human Machine Interfaces
The Use of Metaphor in the User Interface
MONDAY, JANUARY 27, 1997
Instructor: G. Bowden Wise
Rensselaer Polytechnic Institute
mailbox, post office, answering machine
Metaphor is an integral part of our language and thought.
We encounter metaphor:
Metaphor is ubiquitous
Metaphors function as natural models, allowing us to take our knowledge of familiar, concrete objects and experiences and use it to give structure to more abstract concepts.
The purpose of using a metaphor in the user interface is to help the user have a better understanding of the system, its functionality, and its operation. The metaphor helps the user form an accurate mental model.
A model helps the user (and the designer!) understand how the system works making it easier for the user to determine:
The first step is to build a model of the system.
Identify user's problems
There is no one metaphor that can model all aspects of the system functionality. Therefore, identify which parts or features of the system are most likely to cause the user difficulty.
The best way to do this is to observe your users. If you are designing a new system, you can use user interface prototypes - these can be paper mock-ups or actual UI prototype software - and then observe your users using the system through the prototype.
For an existing system, you may already be familiar with the parts of the system which give the user the most trouble due to feedback already obtained. But, should you modify the model in any way, you should still observe your users using the new model.
Find an appropriate metaphor.
Once the model has been developed, find an appropriate metaphor.
Remember that your end users may not be as technical as you, the designer. Therefore, be careful about choosing metaphors that are familiar to you, but not your users.
Choose a metaphor that is appropriate for your end users.
Once you have come up with several metaphors, you may wish to determine how appropriate each of them are. Here are some characteristics that can be used to evaluate a metaphor.
How much structure does the metaphor provide?
By structure we mean concepts and ideas with in the metaphor domain that can be used to help explain the model.
For example, the newspaper metaphor contains all kinds of concepts: editions, delivery routes, subscribers, delivery people, editors, etc.
Similarly, the TV broadcast metaphor also has a lot of structure: channels, cable provider, VCR, shows, stations, reruns, premiere, etc.
Applicability of structure.
How much of the metaphor is relevant to the problem?
Will the metaphor mislead the user into getting a false understanding of the model or how the system works?
Representability of the metaphor.
Is the metaphor easy to represent in the user interface?
Does the metaphor have distinctive visual or auditory elements or representations that can be used when you implement the user interface?
Suitability of the metaphor.
Will your users understand the metaphor? Are they familiar with it?
Note that you may have a metaphor that satisfies all of the other criteria above, but if the metaphor is not suitable it will be useless to your users.
How do you determine if the metaphor is suitable? Observe your users!
Extensibility of the metaphor.
What else does the metaphor buy you?
Does the metaphor have useful bits of structure that may be useful later on?
Does the metaphor extend itself?