1 Task-based user interface principles Fraser Hamilton Brighton University

2 The story so far  What are principles?  S: “Laws”  D: Attributes that contribute to usability  E: Prescriptions to enable performance guarantees  Why bother?  To inform design decision making  Steamline development. Reduce iteration.  Reuse knowledge  Reduce business risk. (More predictable.)

3 Remember this?  Science  Factors that matter: psychology, e.g. redundancy  Design  Guidelines, e.g. “Don’t use colour without…”  Principles, e.g. flexibility, recoverability  Engineering  Users, Tasks, Machines, Performance.  Highly specific advice

4 Bringing home the bacon  Guide designers in making design decisions  Know the consequences of decisions  Relevantto design practice and usability  Validatedconsequences should be known  Predictive… predicted in this context (UTM)  Scopedset of applicable design problems  Prescriptiveinform design  Operationaltechniques to apply them

5 Task based design  Design decisions must be made  What tasks are essential? Omitted?  How should tasks be allocated?  Structure: goals/subgoals, object relations  Representation of objects  How can we inform these decisions?  Performance: learning, usage, improve task output Existing users and artefacts Current task model Envisioned task model User interface design

6 The Analysis-Design gulf  TA produces descriptions The problem: How to use descriptions of user tasks to design systems Descriptions Systems goalsscreen layout taskswidgets objectscommand names

7 What you must know  What are the principles?  What is their theoretical base?  How do they inform interface design?  Scope: Users, Tasks, Machines (i.e. UTM)  How do they improve performance?  How were they validated?  How easy would it be for designers to use them?

8 Task Knowledge Structures (TKS)  Tasks  activity, agents, state  grouped by roles Fraser (Lecturer) ResearcherTutorConsultant Prepare lectures Visit students Hold supervision meetings Mark assignments

9 TKS: Objects  Describe users’ knowledge of objects in a domain Items for sale Audiobook Book Magazine “Brighton Rock”“Noddy and the goblins” “Human Computer Interaction”

10 TKS: Goals  Describe users’ knowledge of goals  Hierarchy, control relations Take a book order Enter order details Send order to publisher Enter customer details Enter book details Get deposit

11 The principles  Taxonomic categorisation  Actions on same/similar objects chunk into a subgoal  Sequential dependency  Actions sequentially related chunk into a subgoal  Easier recall of items, performance benefits

12 Results: Task times

13 Results: task errors

14 How good is the bacon?  TheoryTKS + categorisation  RelevantTA, structure, GUI design  Validatedexperiments  Predictivepredict learning difficulties  Scopedexisting domain K. Gui  PrescriptiveTA + P -> TM -> GUI  OperationalHmm? What objects? Rep?

15 Unprincipled task model

16 Unprincipled design

17 Sequential dependency condition

18 Principled task model

19 Principled GUI