CM160 Foundation of HumanComputer Interaction Representing Design 1

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CM160 Foundation of Human-Computer
InteractionRepresenting Design 1

• Moving from Requirements Analysis to Design
  Analysis
• What is Design Rationale?
• Design Space Analysis

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From Requirements to Design(s)

• Requirements
• a statement about an intended product that
  specifies what it should do or how it should
  perform
• Functional, Data, Environment, User, Usability
  (see previous lecture)e.g. The device must be
  small enough to be carried
• May be seen as a series of questions
• What size should the device be?
• How heavy?
• How much room is available for display?
• How much room is available for input?
• What method of input is best? Etc.

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From Requirements to Design(s)

• Design
• A specification for a product that satisfies the
  requirements
• Not possible to jump straight from requirements
  to design
• Requirements raise questions
• Questions require answering
• Process of discovering the right answers is
  designing
• 2 ways to engage in design
• ignore requirements, do what you want, hope for
  the best
• explore the requirements, test your ideas, talk
  to other designers users, get it right
• All design decisions should be
• linked to requirements (justifiable)
• evaluated (tested justified)

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From Requirements to Design(s)

• Example
• You need a greenhouse.
• It doesnt need to be big.
• It needs to be relatively cheap.
• Increasing size will increase cost
• Increasing quality will increase cost
• A small high-quality greenhouse may cost more
  than a big low-quality one
• Which is most important
• Size? Doesnt need to be big
• Cost? Needs to be relatively cheap
• Durability? Dependent on what you can get for
  available money.
• How can we do this when there are many factors to
  consider?

size
cost
Durability of material
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From Requirements to Design(s)

• Decision Making
• The greenhouse will be small
• Cost dependent on size
• Needs to be cheap
• Therefore small cheap (?)
• But durability has not been specified
• Cheap nasty short life
• Small good quality longer life
• Good quality higher cost
• Trade-off
• If money highest priority
• Aim to spend least amount possible
• Must accept poor quality short life
• If size most important
• Aim to get small but good quality
• Must pay more for longer life
• You cant always satisfy all requirements
• Need to prioritise needs
• Need to justify decisions

size
cost
Durability of material
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Design Rationale

• Design rationale is either
• The process of choosing among design alternatives
  
• A document explaining why certain design
  decisions are made
• Benefits
• Enables alternatives to be discovered
• Enables alternatives to be considered
• Improves communication between designers and
  users
• Identifies the existence of trade-offs
• solution A will work but it doesnt satisfy user
  needs
• solution B satisfies user needs but will take
  longer to develop

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Presenting Design Rationale

• Design Space Analysis
• Where there are several options
• consider goals (requirements) that each option
  would achieve (satisfy)
• Actively encourages designers to explore
  alternatives and examine them closely
• Notation (QOC)
• Questions, Options, Criteria
• Method
• For each issue (requirement)
• List all possible options
• List positive criteria (benefits gained, or goals
  achieved by choosing one or more option)
• show which criteria argue for or against each
  option
• Pick the option that best meets goals

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Design Space Analysis

• Example 1.
• You need to cross a deep wide river quickly, as
  cheaply as possible, without getting your feet
  wet.

Question
Options
Criteria
Build a bridge
Quick
Buy a boat
How can I cross the river?
Rent a boat
Cheap
Borrow a boat
Swim
Dry
Paddle
Which options satisfy all criteria?
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Design Space Analysis

• Example 1.

Question
Options
Criteria
Build a bridge (1)
Quick
Buy a boat (1)
How can I cross the river?
Rent a boat (3)
Cheap
Borrow a boat (3)
Swim (2)
Dry
Paddle (2)
Renting or borrowing a boat meet 3 criteria
each. Explore these options further.
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Design Space Analysis
Question
Options
Criteria
Further Consideration
Quick How quickly can I rent a boat?
How quickly can I borrow a boat?
Rent a boat
How can I cross the river?
Cheap How much will it cost? If
I borrow a boat it might cost nothing.
Borrow a boat
Dry Since all boats will keep me dry I no
longer need to consider this criterion.

• Possible Solutions
• 1. Borrow boat at no cost
• 2. Borrow boat at low cost
• 3. Rent boat at medium cost

Trade-offCost is a primary consideration but may
be traded-off against time if rented boat is
available sooner.
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From Requirements to Design(s)
Consider Design Principles Usability Heuristics
as candidate criteria
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Design Rationale

• Design rationale is critical in interface design
  because
• There are usually numerous alternatives
• Unless analysis is systematic, one may
• pick a suboptimal alternative
• not even think of some alternatives
• Alternatives depend on context
• If the context changes you can
• quickly study the reasoning
• decide if a system change is necessary

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Design Rationale

• As a minimum, use design rationale when
• There is deliberation over a decision
• Reviewers raise issues
• Experts or users
• Opinion war is looming
• You need to accommodate another point of view
• Specialist knowledge is applied
• Testing reveals shortcomings
• Uncertainty remains