Norman’s Gulfs of Execution and Evaluation
The user formulates a plan of action, which is then executed at the computer interface. When the plan, or part of the plan, has been executed, the user observes the computer interface to evaluate the result of the executed plan, and to determine further actions
To get something done…
Start with a goal – the goal that is to be achieved
Take action to manipulate something
Check against your goal
MODELS OF INTERACTION-EXECUTION
The seven stages of action
1.Forming the goal
Something to be achieved
E.g. “make a nice meal”
2.Forming the intention
Specific statements of what has to be done to achieve the goal
E.g. “make a chicken casserole using a can of prepared sauce”
3.Specifying an action sequence
The precise sequence of operators that must be performed to effect the intention
E.g. “defrost frozen chicken, open can”
4.Executing an action
Actually doing something
E.g. “opening the can”
5.Perceiving the state of the world
Perceiving what actually happened
E.g. the experience of smell, taste and look of the prepared meal
6.Interpreting the state of the world
Trying to make sense of the perceptions available
E.g. putting those perceptions together to present the sensory experience of a chicken casserole
7.Evaluating the outcome
Comparing what happened with what was wanted
E.g. did the chicken casserole match up to the requirement of “a nice meal”?
INTERACTION STYLE
Dialog between the computer and user.
Identification of interaction styles:
-Command Line Interface
-Menu
-Natural Language
-Question/ answer and query dialogue
-form -fills and spreadsheets
-WIMP
INTERACTION STYLE- COMMANDLINE
First interactive dialog style to be used
A mean of expressing instruction to the computer directly using function keys, single characters, abbreviations or whole word command
user responds to a prompt on the screen by entering an appropriate command
Benefits of command line:
It offers direct access to system functionality
Quick to use.
The command can be applied to many objects at once
Easily extensible
Suitable for experience user
Disadvantages of command line:
Difficult to use
Difficult to learn
Difficult for error correction
Difficult for novice user
Text only data representation
Hint: using consistent and meaningful commands and abbreviations
Design guidelines:
Offer maximum flexibility
-Conduct task analysis to determine the necessary commands
-Facilitate command remembering
Use meaningful, descriptive names
-Use consistent format of the command line
-Provide on-line help
Facilitate error correction
-Give feedback on both successful and unsuccessful commands
INTERACTION STYLE-MENUS
A set of options displayed on screen
Relies on recognition rather than recall
Benefits of Menus:
Easy to use, reduces memorisation
Structure the user’s decisions
Easy to program
Disadvantages of Menus:
Limited choices per menu
Slow to use in large systems
Multi-user systems
-slow response times
Can take up a lot of space
Design guidelines:
Group logically related options
Various categories of grouping:
-Alphabetical
-Categorical
-Conventional
-Frequency
Limit options to 7 per menu approximately, or break into sections
Avoid excessively deep hierarchies
Options that are not available at a given time should be faded (grayed).
INTERACTION STYLE-QUESTIONS AND ANSWERS
Consists of computer prompt, i.e. question, set of choices, and a response from the user.
Next question may depend on previous answer given.
Benefits of Q&A:
Easy to use for naïve and novice users
Conversational systems
Computer initiated and controlled dialogue
Disadvantages of Q&A:
Slow to use
-Time to read
there is limited support for going back to correct errors that might have been made in earlier questions.
Generally they are quite slow to use - every question must be answered in order to get through the sequence
Design guidelines:
Only one question at a time
Re-display previous answer (s) if replies are linked
Keep sequences compatible with source document or user task model
Display format of acceptable responses
INTERACTION STYLE-FORM-FILLS
Designed for clerical workers
Requires little experience with computers
To enable them to carry out repetitive clerical data collection tasks.
Mimicked paper forms in order to retain the characteristics of the manual task
Designed for a specific type or task.
Advantages
-Forms offer a neat, structured way of gathering information.
Disadvantages
-A form has to be designed specifically for each task.
Users will require a certain level of typing skill
Design guidelines:
Text box :
-Maximum size of text-box can be determined beforehand.
In many fields it is possible to provide a default value for a data field
In some forms, certain values might be required, other optional.
-For required items, program might not proceed to other fields until value is entered.
Interdependencies can be incorporated in the program.
-For example, if one element asks if user is pregnant, then 'female' is automatically entered in the 'sex' field.
INTERACTION STYLE-WIMP
Windows, icons, menus and pointers
The user carries out some physical action (e.g. clicking, dragging) rather than typing commands with complex syntax
The results of the action are seen immediately and, usually, actions are reversible
Advantages:
Novices can learn the basic functions quickly, usually through demonstration and practice rather than from formal instruction or a manual.
Intermittent users can retain the main operational concepts of the interface because it involves visual recognition.
Error messages are rarely needed because most actions are reversible.
There is immediate feedback as to whether or not the user's goals have been achieved.
Users are less anxious, again because they know actions can be reversed.
SUMMARY
Interaction is the heart of all modern interfaces and is important at many levels from the ordering of screens to the clicking of a button.
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