1.
Unit V: HCI in the System
Process
LESSON 01: THE SOFTWARE LIFECYCLE

2.
HCI in the System Software
 Software engineering and the design process for interactive systems
 Usability engineering
 Iterative design and prototyping
 Design rationale

3.
The Software Lifecycle
 Software engineering is the discipline for understanding the software design
process, or life cycle.
 Designing for usability occurs at all stages of the life cycle, not as a single isolated
activity.

4.
The Waterfall Model

5.
Activities in the Life Cycle
Requirements Specification
 designer and customer try capture what the system is expected to provide can be expressed in
natural language or more precise language, such as a task analysis would.
Architectural Design
 High level description of how the system will provide the services required factor system into
major components of the system and how they are interrelated needs to satisfy both functional
and non-functional requirements.
Detailed Design
 Refinement of architectural components and interrelations to identify modules to be implemented
separately the refinement is governed by the non-functional requirements.

6.
Verifications and Validations
Verification
 Designing the product right.
Validation
 Designing the right product
The Formerly Gap
 Validation will always rely to some extent on subjective
means of proof.
Management and Contractual Issues
 Design in commercial and legal contexts.

7.
Life Cycle for Interactive Systems

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 content
 Measuring method
 Now level/ worst case/ planned level/ best level
Problems
 Usability specification requires level of detail that may not be possible early in design
 Satisfying a usability specification does not necessarily satisfy usability.

9.
Part of a Usability Specification for a VCR

10.
ISO Usability Standard 9241
 Adopts traditional usability categories:
 Usability
- The effectiveness, efficiency and satisfaction with which specified users achieve specified goals in
particular environments
 Effectiveness
- The accuracy and completeness with which specified users can achieve specified goals in particular
environment.
 Efficiency
- The resources expended in relation to the accuracy and the completeness of goals achieved.
 Satisfaction
- The comfort and acceptability of the work system to its users and other people affected by its use.

11.
Some metric from ISO 9241

12.
Criteria by which measuring method can
be Determined
 Time to complete the task
 Percent of task complete
 Percent of task completed per unit time
 Ratio of successes to failure
 Time spent in errors
 Percent or number of errors
 Percent or number of competitors better than it
 Number of commands used
 Frequency of help and documentation use
 Percent of favourable/unfavourable user
comments
 Number of repetitions of failed commands
 Number of runs of successes and of failures
 Number of times interface mislead the user
 Number of good and bad features
 Numbers of available commands not invoked
 Number of regressive behaviors
 Numbers of users preferring your system
 Number of times users need to work around a
problem
 Number of times user losses control of the
system.

13.
Iterative design and Prototyping
 Overcomes inherent problems of incomplete requirements
 Prototype
- Simulate or animate some features of intended systems
- Different types of prototype
--Throw-away
--Incremental
--Evolutionary
 Management issues
- Time
- Planning
- Non-functional
- contracts

14.
Techniques for Prototyping
 Storyboards – needs not be computer based and can be animated.
 Limited Functionality Simulations – some part of systems functionality provided by
designers tools like HyperCard are common for these Wizard Oz technique.
 Warning about iterative design
Design inertia – early bad decisions stay bad
Diagnosing real usability problems in prototypes and not just the symptoms.

15.
Design Rationale
 Design Rationale is information that explains why a computer system is the way it
is.
Types of DR
 Process oriented – preserves order of deliberation and decision-making
 Structure-Oriented – emphasizes post hoc structuring of considered desired
alternatives
- Example
- - Issue-based information system (IBIS)
- Design space analysis

16.
Issue-based Information System
 Based 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 position and issues.
 Gibis is a graphical version.

17.
Structure of gIBIS

18.
Design Space Analysis
 Structure- oriented
 QOC – hierarchical structure
 DRL – similar to QOC with a larger language and more formal semantics.

19.
The QOC Notation

20.
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 a design for users.
 Designers identify tasks system will support.
 Scenarios are suggested to test task.
 Users are observed on systems
 Psychological claims of system made explicit
 Negative aspects of design can be used to improve next iteration of design.