Norman's Theory

Norman (1986 - 1988) formulated that any actions of interactions between humans and computers consist of 7 cyclic stages that can then be categorised into 2 gulfs that a designer must overcome:

Gulf of Execution - design the system to ease the process of getting from the intention to the execution.
	1. Forming a goal
	2. Forming an intention
	3. Specifying an action
	4. Executing the action
Gulf of Evaluation - design the system to ease the interpretation and evaluation of the system response for the user after interaction.
	5. Perceiving the state of the system
	6. Interpreting the state of the system
	7. Evaluating the outcome

To address this problem, the below four design principles were formulated:

1.	Make things visible
2.	Use natural mappings
3.	Give feedback
4.	Provide a good conceptual model (perhaps through the use of metaphores)

Natural design concepts shown below are to help designers adhere to Norman's four principles above:

1.	Perceived affordance
	The possible perceived actions of an object.
2.	Mappings
	A relationship between an objects controls and the affects of the control.
3.	Constraints
	Limitations to the possible actions of an object.
4.	Conventions
	Cultural elements that a shared group have become accustom to.
5.	Feedback
	Provide continuous acknowlegement of users actions.

Metaphores
Because people have already developed mental models of physical elements in the world, such as the operation of a table or a bin, designers are able to utilise these mental models when designing a system. The PC 'Desktop' metaphor is an excellent example of how designers are able to capture an existing mental model of a desktop and implement it into a design where users recognise a trash can, and a folder. However, if metaphors are used wrongly, users may find themselves confused as their mental models have been disturbed. A classic example of this involves the Macintosh 'Trash Can' where both deleting and ejecting a disk involves the same process.

By applying Norman's Theory into the design process, designers are able to provide an improved system where users will be able to browse a website without confusion, uncertainty, or disorientation.