what is a good length of string? –depends on its use how do you design a good length of string?...
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• What is a good length of string?– Depends on its use
• How do you design a good length of string?– Can be determined by a process
• What is a good user interface?– Depends on its use
• How do you design a good user interface?– Can be determined by a process
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The Task-Centered Design Process
• figure out who's going to use the system to do what
• choose representative tasks for task-centered design
• plagiarize• rough out a design• think about it• create a mock-up or prototype
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The Task-Centered Design Process (Continued)
• test it with users• iterate• build it• track it• change it
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Figure Out Who's Going to Use the System to Do What
• industry terminology: “task and user analysis.” “personas” “user experience"
• need for task analysis goes beyond “doing what's needed”
• traditional requirements analysis can miss a multitude of interface considerations
• understanding of the users themselves is equally important
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• task and user analysis requires close personal contact between members of the design team and the people who will actually be using the system. this is hard but: “It's certain, however, that early and continued contact between designers and users is essential for a good design.”
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Some practical issues
• Who are the users?
• What are ‘needs’?
• Where do alternatives come from?
• How do you choose among alternatives?
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Who are the users/stakeholders?• Not as obvious as you think:
– those who interact directly with the product– those who manage direct users– those who receive output from the product – those who make the purchasing decision – those who use competitor’s products
• Three categories of user (Eason, 1987): – primary: frequent hands-on– secondary: occasional or via someone else– tertiary: affected by its introduction, or will influence
its purchase
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Who are the stakeholders?Check-out operators
CustomersManagers and owners
• Suppliers• Local shop
owners
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Choose Representative Tasks for Task-Centered Design
• In contrast to software engineering's formal specifications
• formal specification don't work because people are unpredictable
• representative tasks keeps the design focused on users and usability
• Choosing these becomes easier if you've done a good job in step one.
• They must be real task actually described by the users
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Choose Representative Tasks
• Tasks should completely cover the functionality of the system
• can make a checklist of functions and compare those to the tasks to ensure that coverage has been achieved.
• Examples– for a word processor: “transcribe a memo and send it to a
mailing list” – for a spreadsheet: “produce a salary budget for next year” – for a communications program: “login to the office via modem” – for an industrial control system: “hand over control to next
shift”
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Plagiarize
• Not in the legal sense, of course• Find existing interfaces that work for users and
then build ideas from those interfaces into your systems
• People will be able to learn your system faster if is like something they already know.
• Look past the requirements of your system; the “best” solution for your system may not work if inconsistent with other systems the users have.
• Stick to what the user knows if possible, but look for improvements.
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Rough Out the Design
• Don't commit too early• Don't program yet• Sketch ideas... explore alternatives• Check your design against the
representative tasks
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Think About It
• Formal analysis methods are available and may help.
• Examples– Action analysis (GOMS modeling)
• counting keystrokes and mental operations
– Cognitive walkthroughs
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Create a Mock-Up or Prototype
• Need to begin to show the users something
• Even low fidelity prototypes reveal problems and misunderstandings.
• Wizard of OZ emulation can be effective.
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Test the Design With Users
• Users think aloud while doing representative task.
• Record time, errors, problems or surprises.
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Iterate
• Test to improve, not prove (e.g. change it and test again)
• Severe problems may even require a re-examination of the tasks and users
• Iterate until:– usability objectives have be been met– management decides benefit of further
improvement is less than cost of not getting product to market
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Build the Design
• Build for change (modular object oriented style is best)
• If using RAD tool (i.e. UIMS) for prototypes much is already done
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Track the Design & Change the Design
• Designers should not be isolated from the marketplace (the real customers).
• Designer must have contact with users after the design hits the street
• interactions with users can also yield surprises about other applications that have been found for the product
• results in better task descriptions for the next revision
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Managing the Design Process
• Task-Oriented Vs. Waterfall Design – waterfall does not allow the iterations
needed for a deep understanding of the user’s task
• The Design Team – they need to care about users– they need to have experience with both bad
and good interfaces– they need to be committed to and optimistic
about creating an effective system
• Responsibility should be centralized
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Summary
Four basic activities in the design process1. Identify needs and establish requirements2. Design potential solutions ((re)-design)3. Choose between alternatives (evaluate)4. Build the artefact
User-centered design rests on three principles1. Early focus on users and tasks2. Empirical measurement using quantifiable &
measurable usability criteria3. Iterative design