Patterns for HCI and Cognitive Dimensions: two halves of the same story? PPIG 14 th Annual Workshop Brunel University June 2002

2 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

3 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 PARAGRAPHwhich 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 DIAGRAMshows the solution in the form of a diagram A CLOSING PARAGRAPH shows how this pattern fits with other, smaller patterns

7 What about patterns for HCI? Driven by a search for form Problems: Paucity of domain of artefact Invariance Structuring principle

8 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)

10 From Here to Eternity Self Home Town Work Land Love Travel War Belief Space

12 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

13 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”?

14 Placeholder

15 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 …”

16 The Desert House

Frank Lloyd Wright’s Baghdad

18 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