Design Principles, Guidelines and Metaphor Howell Istance Department of Computer Science De Montfort University

SOFT Interactive Systems Objectives n to provide an overview of Norman's model of interaction n to distinguish between user model, design model and system image n to explain basis for common design principles in HCI n to explain the role of metaphor as one means of building an appropriate user model

SOFT Interactive Systems The DMU PABX interface… The university installed an well known PABX telephone system - the functionality provided is hardly used at all by staff despite regular attempts to publicise the features by printing and circulating the list of key codes and the actions they cause. Why it this so….?

SOFT Interactive Systems Fundamental requirements of good design for use by people n provide a good conceptual model n make things visible n use easily understood mappings

SOFT Interactive Systems Affordances and Constraints n affordance - the perceived and actual properties of a thing, primarily those fundamental properties that determine just how the thing could possibly be used n when affordances are well utilised, the user can easily guess what to do by looking at the thing (no picture, label or instruction is needed) n constraints suggest natural limitations in the way in which things can be used

SOFT Interactive Systems Mapping and Feedback n mapping relationship between controls and their movements, and the results in the real world n natural mappings utilise physical analogies and cultural standards u additive dimensions u substitutive dimensions n feedback: sending the user information about what action has actually been done and what has been achieved

SOFT Interactive Systems Norman's Theory of action n n bridging the gulf of execution - designer creates input structures and information displays to fit the psychological needs of the user n bridging the gulf of evaluation - user has intentions, creates plans and action sequences in terms of what is required by the system (the way the designer intends the system to be used) Interpreted psychological variables (users knowledge) physical variables (controlled by system) translated into actions (gulf of evaluation) (gulf of execution)

SOFT Interactive Systems Stages of user activities n establishing the goal n forming the intention n specifying the action sequence n executing the action n perceiving the system state n interpreting the state n evaluating the state with respect to the goals and intentions

SOFT Interactive Systems n (illustration of 7 stage model)

SOFT Interactive Systems n (fridge example)

SOFT Interactive Systems Problems with the refrigerator example n matching the psychological variables of interest to the physical variables being controlled - labels on the control mechanism indicate some relationship to the psychological variables, they do not control these directly n mapping - strong interaction between controls make a simple mapping between control function and control outcome difficult to establish and represent n feedback - very slow n conceptual model - none, instructions do not convey an appropriate model

SOFT Interactive Systems User Model Design Model Design Model, User Model and System Image Designer User System and Documentation System Image

SOFT Interactive Systems Developing key interface elements n develop an appropriate interface metaphor or conceptual model suitable to the user population n communicate that model to the user in a consistent manner n provide high level task-oriented operations, not low-level implementation commands (bridge the gap of execution) n make things visible (if an object has function (behaviour), the interface should show this) n provide informative feedback

SOFT Interactive Systems Communicating Models

SOFT Interactive Systems Metaphors n can be used to structure a user's mental model to facilitate ease of initial learning n use existing knowledge of familiar domains to provide explanations of unfamiliar artifacts n many terms in computing rely on common-use metaphors u e.g menus, forms, windows n provides the designer with a means of building a 'myth' that the system behaves like something the user is already familiar with

SOFT Interactive Systems 2D spatial metaphors n sheet of paper, forms, spread sheets n pages - hold text, images, (magically) moving images n drafting table - tools laid out around a working area n light table - view many small images at once n maps - birds eye view n blackboards and whiteboards

SOFT Interactive Systems 2 1 / 2 spatial metaphors n uses several layers of stacked 2D surfaces -each congruent with the overall metaphor n desktops and briefcases n books n Notebooks n Index Cardfiles, NoteCards n Doors and Rooms

SOFT Interactive Systems Macintosh Desktop

SOFT Interactive Systems....leads to a full wastebasket

SOFT Interactive Systems Components of NoteCards

SOFT Interactive Systems 3D metaphors n virtual worlds n buildings

SOFT Interactive Systems Metaphors based on human activity n Visiting a supermarket, museum, eating in a restaurant n agents - someone who does a task on behalf of someone else n stage and theatre as spatial metaphor

SOFT Interactive Systems Tension between literalism and magic n literal interpretation of the spreadsheet would use an on- screen calculator to sum columns of values for the user to type back into the spreadsheet u maximises understanding but does not add power n magic interpretation - rows and columns magically sum themselves and then display values u maximises power but may interfer with understanding

SOFT Interactive Systems Strengths in the use of metaphors n a strength of using metaphors is that they can suggest behaviours to the user based on their knowledge of the familiar domain and encourage exploratory learning of the new artefact u e.g.. if I throw a file into a waste-basket, I should be able to pick it out again, Now how do I do that...?

SOFT Interactive Systems Limitations in the use of metaphors n by definition, each metaphor has a limitation - one single metaphor is unlikely to represent all aspects of system behaviour n leads to the use of composite metaphors e.g. windows and desk-tops n user has to be encouraged to use relevant parts of the analogy n care has to be taken that the metaphor does not suggest behaviours that can lead to errors

SOFT Interactive Systems Process of generating metaphors (after Erickson) n Define and understand the functionality offered by the system n Observe users understanding of the artifact and identify problems they have n Generate metaphors n Evaluate candidate metaphors using: u Amount of structure metaphor offers u Applicability of structure to artifact u Representability u Suitability to audience u Extensibility

SOFT Interactive Systems MacIntosh Guidelines n metaphor based n direct manipulation n see and point n consistency n WYSIWYG n user control n feedback and dialogue n forgiveness n perceived stability n aesthetic integrity n modelessness

SOFT Interactive Systems Alternative Principles (Genter and Neilsen) n central role of language n rich internal representation of objects n more expressive interface n expert users n shared control