chapter 3 - The Interaction

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Interaction:

the purpose of an interactive system is to aid a user in accomplishing goals from some application domain.

A domain defines an area of expertise and knowledge in some real-world activity. Some examples of domains are graphic design, authoring and process control in a factory.

Tasks are operations to manipulate the concepts of a domain.

A goal is the desired output from a performed task. For example, one task within the graphic design domain is the construction of a specific geometric shape with particular attributes on the drawing surface. A related goal would be to produce a solid red triangle centered on the canvas.

An intention is a specific action required to meet the goal.

The core language describes computational attributes of the domain relevant to the System state, whereas the task language describes psychological attributes of the domain relevant to the User state.

Norman's Model of Interaction:

The interactive cycle can be divided into two major phases: execution and evaluation. These can then be subdivided into further stages, seven in all. The stages in Norman’s model of interaction are as follows:

Establishing the goal.

Forming the intention.

Specifying the action sequence.

Executing the action.

Perceiving the system state.

Interpreting the system state.

Evaluating the system state with respect to the goals and intentions.

First the user forms a goal. This is the user’s notion of what needs to be done and is framed in terms of the domain, in the task(user) language. It is liable to be imprecise and therefore needs to be translated into the more specific intention, and the actual actions that will reach the goal, before it can be executed by the user. The user perceives the new state of the system, after execution of the action sequence, and interprets it in terms of his expectations. If the system state reflects the user’s goal then the computer has done what he wanted and the interaction has been successful; otherwise the user must formulate a new goal and repeat the cycle.

The gulf of execution is the difference between the user’s formulation of the actions to reach the goal and the actions allowed by the system. If the actions allowed by the system correspond to those intended by the user, the interaction will be effective. The interface should therefore aim to reduce this gulf.

The gulf of evaluation is the distance between the physical presentation of the system state and the expectation of the user. If the user can readily evaluate the presentation in terms of his goal, the gulf of evaluation is small. The more effort that is required on the part of the user to interpret the presentation, the less effective the interaction.

it only considers the system as far as the interface. It concentrates wholly on the user’s view of the interaction. It does not attempt to deal with the system’s communication through the interface.

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The Interaction Framework

The nodes represent the four major components in an interactive system – the System, the User, the Input and the Output. Each component has its own language.

The User begins the interactive cycle with the formulation of a goal and a task to achieve that goal. The only way the user can manipulate the machine is through the Input, and so the task must be articulated within the input language. The input language is translated into the core language as operations to be performed by the System.

The System then transforms itself as described by the operations; the execution phase of the cycle is complete, and the evaluation phase now begins.

The System is in a new state, which must now be communicated to the User. The current values of system attributes are rendered as concepts or features of the Output. It is then up to the User to observe the Output and assess the results of the interaction relative to the original goal, ending the evaluation phase and, hence, the interactive cycle.

There are four main translations involved in the interaction: articulation, performance, presentation and observation.

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Ergonomics

ergonomics (or human factors) is traditionally the study of the physical characteristics of the interaction: how the controls are designed, the physical environment in which the interaction takes place, and the layout and physical qualities of the screen.

Arrangement of controls and displays: Sets of controls and parts of the display should be grouped logically to allow rapid access by the user. This may not seem so important when we are considering a single user of a spreadsheet on a PC, but it becomes vital when we turn to safety-critical applications such as plant control, aviation and air traffic control. In each of these contexts, users are under pressure and are faced with a huge range of displays and controls. Here it is crucial that the physical layout of these be appropriate.

The physical environment of the interaction: the physical environment in which the system is used may influence how well it is accepted and even the health and safety of its users. in any system the smallest user should be able to reach all the controls (this may include a user in a wheelchair), and the largest user should not be cramped in the environment.

Health issues: Physical position, Temperature, Lighting, Noise, Time.

The use of color: Colors used in the display should be as distinct as possible and the distinction should not be affected by changes in contrast. Blue should not be used to display critical information. If color is used as an indicator it should not be the only cue: additional coding information should be included. The colors used should also correspond to common conventions and user expectations. Red, green and yellow are colors frequently associated with stop, go and standby respectively. Therefore, red may be used to indicate emergency and alarms; green, normal activity; and yellow, standby and auxiliary function. These conventions should not be violated without very good cause.

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Interaction Styles

CMD

It provides a means of expressing instructions to the computer directly, using function keys, single characters, abbreviations or whole-word commands.

Command line interfaces are powerful in that they offer direct access to system functionality (as opposed to the hierarchical nature of menus), and can be combined to apply a number of tools to the same data. They are also flexible: the command often has a number of options or parameters that will vary its behavior in some way, and it can be applied to many objects at once, making it useful for repetitive tasks.

However, this flexibility and power brings with it difficulty in use and learning. Commands must be remembered, as no cue is provided in the command line to indicate which command is needed. They are therefore better for expert users than for novices.

MENU

In a menu-driven interface, the set of options available to the user is displayed on the screen, and selected using the mouse, or numeric or alphabetic keys. Since the options are visible, they are less demanding of the user, relying on recognition rather than recall. However, menu options still need to be meaningful and logically grouped to aid recognition. Often menus are hierarchically ordered, and the option required is not available at the top layer of the hierarchy.

NATURAL LANGUAGE

systems can be built to understand restricted subsets of a language. For a known and constrained domain, the system can be provided with sufficient information to disambiguate terms. It is important in interfaces which use natural language in this restricted form that the user is aware of the limitations of the system and does not expect too much understanding. Language is by nature vague and imprecise: this gives it its flexibility and allows creativity in expression. Computers, on the other hand, require precise instructions.

Question and answer dialog is a simple mechanism for providing input to an application in a specific domain. The user is asked a series of questions (mainly with yes/no responses, multiple choice, or codes) and so is led through the interaction step by step. An example of this would be web questionnaires. These interfaces are easy to learn and use, but are limited in functionality and power. As such, they are appropriate for restricted domains (particularly information systems) and for novice or casual users