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Patterns for HCI and Cognitive Dimensions: two halves of the same story?

PPIG 14th Annual Workshop

Brunel University

18-21 June 2002

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What are patterns?

• A way of capturing good design practice• A way of developing a common design vocabulary• Structured around problems designers face

“Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice”

• Not created or invented, but harvested• A pattern language is composed of patterns in

relationship to each other

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Alexandrian Pattern form

• NAME (usually describes the effect of using the pattern)• A PHOTOGRAPH showing an archetypal example of the pattern

in use • AN INTRODUCTORY PARAGRAPH which sets the pattern in

the context of other, larger scale patterns• THE HEADLINE an encapsulation of the problem (one or two

sentences)• THE BODY of the problem (this can be many paragraphs long)• THE SOLUTION the heart of the pattern, always stated in the

form of an instruction• A DIAGRAM shows the solution in the form of a diagram• A CLOSING PARAGRAPH shows how this pattern fits with other,

smaller patterns

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What about patterns for HCI?

• Driven by a search for form

Problems:• Paucity of domain of artefact• Invariance• Structuring principle

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What is A Structuring Principle and why is it important?

• Engineer’s Sketchbook (Thomas Walter Barber)• From Here to Eternity (Andrew Motion)• Periodic Table (Dimitri Mendeleev)

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From Here to Eternity

• Self• Home• Town• Work• Land• Love • Travel• War• Belief• Space

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What are Cognitive Dimensions?

• A set of concepts that describe notational systems• Created to give designers a common vocabulary• “Broad brush” and written in apprehensible language• Focussed on users & their tasks

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What about use of Cognitive Dimensions?

• Exemplification of use• Expression of “places” along dimensions

• Even exemplars of “ends” of dimensions

• How do they actually operate “for real”?

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Placeholder

<Insert WP “form” slides here>

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Language of Cognitive Dimensions

• “I like to compare the cussedness of information structures with the behaviour of ideal gases. Three quantities, temperature, pressure and volume, describe an ideal gas. If you want to increase the temperature, you can keep the pressure constant (but the volume must be allowed to increase) or you can keep the volume constant (but the pressure must be allowed to increase). Taken in pairs, these three dimensions are orthogonal. But you cannot raise the temperature while holding constant both the pressure and the volume”

• “…CDs are not supposed to be good or bad …”

• “It ought to be possible to consider each dimension and say ‘if you change the design in the following way, you will move its value on this dimension’ …”

• “ … it should be possible to describe the characteristics of a dimension without any evaluative emphasis …”

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The Desert House

Frank Lloyd Wright’s Baghdad

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One Story?

Patterns for HCI

• Rich expression of form• Strong call to value• Small “pool” of examples to

harvest from• No structure (or “invariance”)

Cognitive Dimensions

• Rich expression of invariance• Strong mapping of space• Large “pool” of applicable

artefacts• No “form”; no call to value