Preece Chapter 7.7 & Mc Cracken Chapter 3 Task Analysis Preece Chapter 7.7 & Mc Cracken Chapter 3 JTBurns 2004

User interfaces are designed for.. a new system to replace an existing manual system e.g. library information system an existing computer system being redesigned functionality remains the same functionality is extended or changed in some way. a completely new system with no manual equivalent (generally rare) There is usually some situation with existing users and usage that can be studied and analysed. JTBurns 2004

Task Analysis provides an essential basis for early stages of interface design evaluation of design at early and late stages structuring training in system use structuring and design of documentation JTBurns 2004

Levels of Task Analysis relate to existing situation or new system. General Analysis of User Characteristics Detailed Analysis of tasks in present job(s) Subset of tasks to be included in new system Analysis of Actions and Objects in new system JTBurns 2004

General Analysis level who are the users classify the users into one or more groups define characteristics of the group what are the main task components of the users’ present job what proportion of time is spent in different tasks what causes variations in this where are the tasks carried out what equipment (other than the computer system) are used what communication is there between the user and other people JTBurns 2004

Detailed analysis of tasks in present job what is the hierarchical structure of main tasks, and subtasks within these main tasks how do users see the structure of their job in terms of tasks for each task identified what information is required what actions arise or result from decisions what feedback is provided on effect of actions what affects successful performance what are the possible errors and what factors cause these JTBurns 2004

Requirements for a task analysis method a structure to represent goals, subtasks, procedures, objects and actions a means of collecting data from experts in the task domain a means of representing the analysis to check validity of the analysis back with experts communicate with others in design team guidance for mapping the analysis to the design JTBurns 2004

Detailed analysis of tasks in present job what are the good features of the existing system which should be retained in the subsequent redesign what are the bad features of the existing system that should be designed out what skills are required for each task how are the required skills trained initially and how are these retained JTBurns 2004

Objectives of task analysis to support interface design identify a hierarchy of user goals, tasks and subtasks together with a plan describing how and when these are done represent lowest level task as a set of procedures include statements of information requirements and exception conditions identify set of actions and associated objects JTBurns 2004

Hierarchical Task Analysis Involves breaking a task down into subtasks, then sub-sub-tasks and so on. These are grouped as plans which specify how the tasks might be performed in practice HTA focuses on physical and observable actions, and includes looking at actions not related to software or an interaction device Start with a user goal which is examined and the main tasks for achieving it are identified Tasks are sub-divided into sub-tasks JTBurns 2004

Example Hierarchical Task Analysis 0. In order to borrow a book from the library 1. go to the library 2. find the required book 2.1 access library catalog 2.2 access the search screen 2.3 enter search criteria 2.4 identify required book 2.5 note location 3. go to correct shelf and retrieve book 4. take book to checkout counter JTBurns 2004

Example Hierarchical Task Analysis (plans) plan 0: do 1-3-4. If book isn’t on the shelf expected, do 2-3-4. plan 2: do 2.1-2.4-2.5. If book not identified do 2.2-2.3-2.4. JTBurns 2004

Example Hierarchical Task Analysis (graphical) Borrow a book from the library plan 0: do 1-3-4. If book isn’t on the shelf expected, do 2-3-4. go to the library find required book retrieve book from shelf take book to counter 1 2 3 4 plan 2: do 2.1-2.4-2.5. If book not identified from information available, do 2.2-2.3-2.4-2.5 access search screen enter search criteria identify required book access catalog note location 2.1 2.2 2.3 2.4 2.5 JTBurns 2004

Hierarchical task analysis (HTA) Structural components goal - statement of a desired state to be achieved e.g. obtain a printed balance from an ATM operation - things done in order to achieve goals e.g. produce a paper copy sub-operations- subordinate operations to attain main operation plan - specifies when the conditions when each sub-operation will be carried out JTBurns 2004

Hierarchical Task Analysis Aim is to describe a task in terms of a hierarchy of operations and plans where operations = Goal-Task-Action plans = specification of conditions under which (sub) tasks are carried out Advantages of HTA simple, informal notation but still requires considerable skills on part of analyst. Can be captured graphically using a form of structure chart JTBurns 2004

Partial HTA chart for Editing Text in Windows 0. Edit Text Plan 1: According to Requirements 1. Cut Text 1. Use Menu option 2. Use Hot-key Combo. 3. Use Toolbar Icon 4. Use Delete Plan 1.2: 1,2 1. Select Text 2. Press Ctrl + X JTBurns 2004

Means of collecting task analysis data interviews with potential users observations of users performing tasks by trained observers activity sampling activity logging (by observer) activity logging (by user) - 'diary of activities' JTBurns 2004