Unit 2 hci in software process

Software Engineering
• Software design process or life cycle called Software Engineering
– that addresses the management and technical issues of the
development of software systems.
– The software life cycle is an attempt to identify every activity that
occur in software development from the initial concept formation
for a software system up until its eventual phasing out and
replacement.
– These activities must then be ordered in time in any
development Project
Dr.S.ROSELIN MARY, HOD/CSE, ANAND INSTITUTE OF HIGHER TECHNOLOGY07-09-2020 1

The waterfall model
Requirements
specification
Architectural
design
Detailed
design
Coding and
unit testing
Integration
and testing
Operation and
maintenance

Activities in the life cycle
• Requirements specification
– Designers try to capture what functionality is expected from the
system
– “HOW” is not concern of this activity.
– Can be expressed in natural language or more precise languages like
Unified Modeling Language.
– begins at the start of product development and the requirements
are from the customer’s perspective
– It involves eliciting information from the customer about the work
environment, or domain, in which the final product will function.Dr.S.ROSELIN MARY, HOD/CSE, ANAND INSTITUTE OF HIGHER TECHNOLOGY07-09-2020 3

• Architectural Design:
– a decomposition of the system that allows independent development of
separate components
– These components will later be integrated
– satisfying both functional and non-functional
requirements after integration
• Detailed Design:
– Designer is responsible to ensure complete functionality of the
component(s) provided by the architectural design phase.

• Coding & Testing:
– Transform detailed design in a programming language.
– Component testing
• Integration & Testing:
– Completed components should be tested individually
– they must be integrated as described in the architectural design.
– Integration testing is performed to ensure correct behavior and
acceptable use of any shared resources e.g. memory

• Maintenance:
– involves the correction of errors in the system which are
discovered after release
– System can be revised to satisfy requirements that were not
realized during previous development.
– maintenance provides feedback to all of the other activities in the
life cycle

Verification and validation
• Verification
– Are you building the product right?
– Software must conform to its specification
• Validation
– Are you building the right product?
– Software should do what the user really requires
• Validation & Verification relies on some proof
– Subjective means of proof i.e User signed Requirements/system
design
– Management contracts
• Time
• Economical issues
• Recourses e.g. Manpower, hardware etc Dr.S.ROSELIN MARY, HOD/CSE, ANAND INSTITUTE OF HIGHER TECHNOLOGY
07-09-2020 7

The life cycle of interactive systems
cannot assume a linear
sequence of activities as in the
waterfall model
• lots of feedback!
• The actual design process is iterative
Requirements
specification
Architectural
design
Detailed
design
Coding and
unit testing
Integration
and testing
Operation and
maintenance
Dr.S.ROSELIN MARY, HOD/CSE, ANAND INSTITUTE OF HIGHER
TECHNOLOGY
07-09-2020 8

Usability engineering
• The ultimate test of usability based on measurement of user experience
• Usability engineering demands that specific usability measures be made explicit
as requirements
• Usability specification
• usability attribute/principle
• measuring concept
• measuring method
• now level/ worst case/ planned level/ best case
• Problems
• usability specification requires level of detail that may not be possible early in
design satisfying a usability specification
• does not necessarily satisfy usability

Part of a usability specification for a VCR
Attribute: Backward recoverability
Measuring concept: Undo an erroneous programming
sequence
Measuring method: Number of explicit user actions
to undo current program
Now level: No current product allows such an undo
Worst case: As many actions as it takes to
program-in mistake
Planned level: A maximum of two explicit user actions
Best case: One explicit cancel action
Dr.S.ROSELIN MARY, HOD/CSE, ANAND INSTITUTE OF HIGHER TECHNOLOGY
07-09-2020 10

ISO usability standard 9241
adopts traditional usability categories:
• effectiveness
• can you achieve what you want to?
• efficiency
• can you do it without wasting effort?
• satisfaction
• do you enjoy the process?
TECHNOLOGY
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Usability
objective
Effectiveness
measures
Efficiency
measures
Satisfaction
measures
Suitability Percentage of Time to Rating scale
for the task goals achieved complete a task for satisfaction
Appropriate for Number of power Relative efficiency Rating scale for
trained users features used compared with
an expert user
satisfaction with
power features
Learnability Percentage of
functions learned
Time to learn
criterion
Rating scale for
ease of learning
Error tolerance Percentage of
errors corrected
successfully
Time spent on
correcting errors
Rating scale for
error handling
ISO usability standard 9241
TECHNOLOGY
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Iterative design and prototyping
• Iterative design overcomes inherent problems of incomplete requirements
• Prototypes
 simulate or animate some features of intended system
 different types of prototypes
• throw-away/ Rapid Prototyping
• Incremental prototyping
• Evolutionary prototyping
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Techniques of Prototyping
• Storyboards:
– is a graphical depiction of the interface without accompanying
system functionality.
– can be animated, If not animated, storyboards usually include
annotations and scripts indicating how the interaction will occur.
• Limited functionality simulation:
– some part of system functionality provided by designers
– tools like HyperCard & Wizard of Oz technique
TECHNOLOGY
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Case Study
• A software solution is required to display information about incoming and outgoing flights
to the public at Palm Island Airport. The airport terminal will have a number of large
display screens (approximately 42" in size, measured horizontally) for viewing by the
public. The display screens will provide information about flight arrivals and departures at
Palm Island Airport.
• It is envisaged that this information will require more than one page. Therefore, each
page will be required to display for not less than 10 seconds, and not more than 15
seconds, before moving onto the next page in the cycle. Each time a page loads, it must
show the latest information available at that time. Airport branding and the current time
and date must also to be shown on all pages that are visible to the public.
• The layout should be designed in such a way that members of the public can quickly find
the appropriate flight and check its status. Any flight that has been cancelled must stand
out. The information should be readable from a distance of not less than four metres. At
peak times, passengers are likely to seek information about one of five flights arriving
and/or departing (potentially ten flights in total: up to five arrivals; up to five departures).
• The solution also requires that administration staff be able to: insert, edit and delete flight
information. The administration user-interface must be intuitive and efficient. The system
must also allow more than one administrator to update flight information simultaneously
(not necessarily details of the same flight). When an administrator completes an update,
that information must be available to the public at the next screen (or page) refresh.
TECHNOLOGY
07-09-2020 18

Case Study (contd)
• The public information necessary about flights arriving is:
– Flight Number
– Where the flight is coming from (eg airport or city)
– Expected time of arrival
– Current status of flight (eg en-route, landed, delayed, cancelled, diverted, contact
operator)
– Gate of arrival
• The public information necessary about flights departing is:
– Flight Number
– Destination of flight (eg airport or city)
– Expected time of departure
– Current status of flight (eg As scheduled, gate open, boarding, last call, gate
closed, airborne, delayed, cancelled, contact operator)
– Departure gate
• The client would also like to make this information accessible to members of the
public when using one of the internet connected information kiosks situated around
the airport, and for users visiting the Palm Island Airport website. Legislation must be
strictly adhered to as applicable (eg as relevant from copyright, data protections,
accessibility and disability discrimination, etc)
TECHNOLOGY
07-09-2020 19

Design rationale
• Design rationale is information that explains why a computer system is the way it is
including its structural or architectural description and its functional or behavioral
description.
 Benefits of design rationale
• communication throughout life cycle
• reuse of design knowledge across products
• enforces design discipline
• presents arguments for design trade-offs
• organizes potentially large design space
• capturing contextual information
TECHNOLOGY
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Types of DR:
• Process-oriented
• preserves order of deliberation and decision-making
• Structure-oriented
• emphasizes post hoc structuring of considered design alternatives
Two examples:
• Issue-based information system (IBIS)
• Design space analysis
TECHNOLOGY
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Issue-based information system (IBIS)
• basis for much of design rationale research
• process-oriented
• main elements:
issues
– hierarchical structure with one ‘root’ issue
positions
– potential resolutions of an issue
arguments
– modify the relationship between positions and issues
• gIBIS is a graphical version
TECHNOLOGY
07-09-2020 22

Structure of gIBIS
Sub-issue
Issue
Sub-issue
Sub-issue
Position
Position
Argument
Argument
responds to
responds to
objects to
supports
questions
generalizes
specializes
TECHNOLOGY
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Design space analysis
• Structure-oriented
• QOC – hierarchical structure:
questions (and sub-questions)
– represent major issues of a design
options
– provide alternative solutions to the question
criteria
– the means to assess the options in order to make a choice
• DRL – similar to QOC with a larger language and more formal semantics
• Decision problem,
• alternatives
• goals
TECHNOLOGY
07-09-2020 24

The QOC notation
Question
Option
Option
Option
Criterion
Criterion
Criterion
Question
… Consequent
Question
…
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Psychological design rationale
• to support task-artefact cycle in which user tasks are affected by the systems they use
• aims to make explicit consequences of design for users
• designers identify tasks system will support
• scenarios are suggested to test task
• users are observed on system
• psychological claims of system made explicit
• negative aspects of design can be used to improve next iteration of design
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Summary
The software engineering life cycle
• distinct activities and the consequences for interactive system design
Usability engineering
• making usability measurements explicit as requirements
Iterative design and prototyping
• limited functionality simulations and animations
Design rationale
• recording design knowledge
• process vs. structure
TECHNOLOGY
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Unit 2 hci in software process

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