1. Software Quality
UNIT - 1

2. Introduction
Software Quality measures how well the software is designed (Quality of design) and how well the software conforms to the design (Quality of conformance)
Where,
Quality of design concerned about the specifications, design and requirements of the software
Quality of Conformance concerned with the implementation of the software

3. Introduction The primary goal of engineering the product is
To improve the quality of the software products
To increase the productivity & Job Satisfaction of the engineers

4. Introduction
Note:
User Satisfaction issue must also be considered for Quality
User Satisfaction = Good Quality + Delivered within budget and Schedule + Complaint product
Most of the developers feel that software quality can be carried out only after the code is generated. But it is not true. It can be enforced each and every stages of a software process

5. Introduction
Note:
If a team stresses quality in all engineering activities,
It reduces the amount of rework
Results in lower cost

6. Introduction
Note:
SQM is the management Technique that can be applied to the development of software to favor the quality
Software Quality comprises of
Quality Control
Quality Assurance
Quality Cost

7. Introduction What is Quality?
It is a characteristic or an attribute of something that must conforms to the design standards
Quality can be a measurable characteristics that can be compared to length, color etc.,

8. Introduction Insight about Quality? Quality is Not absolute
Quality is Multidimensional
Subject to constraints
Quality criteria are not independant

9. Introduction What is Quality? “The degree of Excellence” - OED, 1990
“Zero Defects” – Crosby, 1979
“The totality of features and characteristics of a product or service that bear on its ability to satisfy specified needs” – ISO, 1986
Quality of a product is achieved thro its features & characteristics
So it is associated with the attribute of a product thro which performance can be achieved

10. Introduction Software Quality?
Conformance to explicitly stated functional, performance requirements & development standards and implicit characteristics that are expected by all softwares
Department of Defense defined a SQ as “the degree to which the attribute of the softwares enable it to perform its intended end use”

11. Introduction Software Quality 2 features of quality software:
Conformance to its specification
Fitness to its intended purpose

12. Introduction Software Quality
When compared to other industry, Software Quality will be problamatic coz’
It does not have physical existence
Lack of knowledge of client
Rapid change rate in both hardware & software
High expectation of the customer

13. Introduction Views of Quality Quality is a multidimensional construct
It can be considered as a “Polyhedron Metaphor” where a quality is represented by a 3-dimensional solid & each face represents a different aspects of quality
“Polyhedron Metaphor” is illustrated as

14. Introduction Views of Quality Timeliness Cost Correctness
Functionality
Reliability
Maintainability

15. Introduction Views of Quality
Based on different characteristics of a product, it is been classified into number of views or perspectives
These views may be considered based on external observers viewing towards a product ex: user, supplier or client etc.,
These views are used to vary & conflict based on different types of peoples who is viewing the product
Ex: viewing persons
Project Manager
Business Analyst
Programmer
Quality Auditor
End user
Line Manager and Project Sponsor

16. Introduction Views of Quality
In general, conflicting views are represented between User and Designer
Designer
User
Good Specification
What I want
Technically correct
Fast Response
Easy to maintain
Easy to use help menu
Fast development
Exception data & reporting
Well documented
Input data once
User managed & Well trained
Access to all systems
Simple Menu Structure
Accurate time

17. Introduction Views of Quality
conflicting views are classified into 5 types
Transcendent view
Product based view
Value based view
Manufacturing view
User based view

18. Introduction Views of Quality Transcendent view Value based
Product based
Manufacturing
user based

19. Introduction Views of Quality Transcendent view Product based view
This view relates quality to excellence or elegance.
In large scale projects, it is expensive to innate high degree of excellence
Product based view
Quality  Cost i.e., to build high quality in a product it costs high
This type of quality can be added to a product in 2 ways
Greater Functionality
High Quality Solution thro the use of QMS

20. Introduction Views of Quality Value based view Manufacturing view
This view depends on what price that the customer can afford
With in the software development, this view can be used to add the quality to a product with the help of needed people, time & tools
Manufacturing view
This view measures the quality in terms of conformance to requirements

21. Introduction Views of Quality User based view
This view can be summarized as “Fitness for purpose”
i.e., the intended functionality for the product must be facilitated according to the user

22. Hierarchical Models of Quality
To compare quality in different situations (quantitatively & qualitatively), it is needed to establish a model of quality in hierarchical structure
Ex: Assessment and Reporting method used in School
Student progress report is prepared under series of headings such as Subject name with both qualitative & quantitative assessment
These measures are derived from a examination or a formal test

23. Hierarchical Models of Quality
Hierarchical Model (Cont…)
Traditional Assessment Method
Subject
Teachers Comments
Term
Grade
(A-E)
Exam Mark (%)
English
Maths
Science
Tamil
Social Science
Total

24. Hierarchical Models of Quality
Hierarchical Model (Cont…)
Presently, the assessment of a person has become complicated cos’ a subject may be broken into different level of skills where each of the skills are measured collectively to give a more detailed result i.e.,

25. Hierarchical Models of Quality
Hierarchical Model (Cont…)
Student
Maths
Science
Social
English
Oral Skills
Reading Skills
Writing
Creative
Has evolved into
English

26. Hierarchical Models of Quality
Hierarchical Model (Cont…)
Based on different measures of software, its quality can be depicted as:
Quality factor
Quality criterion
Ex: Maintainability
Ex: Reliability
Ex: Usability
Quality Metrics
Ex of Metrics: Accuracy, Consistency, Error Tolerance
and simplicity

27. Hierarchical Models of Quality
These models are used to identify the needed quality criteria's that can be used in improving the resultant quality of the product
Types of quality models
McCall Model
Boehm Model
FURPS Model
ISO 9126 Model
Dromey Model

28. Hierarchical Models of Quality
Hierarchical Model of McCall
Proposed by McCall in It is also referred as General Electronics model after McCall
This model is originates from US military developed for US Air force
This model can be used during the development process by the system developers
In this model, McCall attempts to bridge the gap between users & developers by focusing number of quality factors that reflect both the user views & developer priorities

29. Hierarchical Models of Quality
Hierarchical Model of McCall
Product
Revision
Transition
Product operations
Portability
Reusability
Interoperability
Maintainability
Flexibility
Testability
Correctness, Reliability, Efficiency, Integrity, and Usability

30. Hierarchical Models of Quality
Hierarchical Model of McCall
McCall model identifies 3 areas of software work or 3 types of quality characteristics
Product operation
Product revision
Product Transition
Product Operation – It explains the working operation of the product that can be learned easily efficiently
Product Revision
- It concerned with error correction of the system
- The system may undergo changes
Product Transition – This is applicable in distributed applications & adaptable to new environments

31. Hierarchical Models of Quality
Hierarchical Model of McCall
McCall defines following 11 quality factors:
Usability
Integrity
Efficiency
Correctness
Reliability
Maintainability
Flexibility
Testability
Portability
Reusability
Interoperability
Execution efficiency
Storage efficiency

32. Hierarchical Models of Quality
Hierarchical Model of McCall
McCall identifies 3 areas of software work in a hierarchy of factors, criteria and metrics
11 factors (To specify) – External view of the software seen by the users
23 criteria's (To build) – Internal view of the software seen by developers
Metrics (To control) – method of measurement

33. Hierarchical Models of Quality

34. Hierarchical Models of Quality

35. Hierarchical Models of Quality
Hierarchical Model of Boehm (1978)
This model is presented by Barry W Boehm
Boehm model defines “set of well defined, differentiated characteristics” of software quality where the quality criteria's are subdivided.
In this first division is named as “general utility” and the next one is “As-is utility” that is the subtype of first one.

36. Hierarchical Models of Quality
Hierarchical Model of Boehm (1978)
It is similar to McCall’s model where a quality of software is structured around
Higher level characteristics
Intermediate level characteristics
Primitive characteristics

37. Hierarchical Models of Quality
Hierarchical Model of Boehm (1978)
Higher level characteristics – it addresses answers for 3 questions:
As-is Utility [How well (easily, reliably, efficiently) can I use as-is?]
Maintainability [How easy is it to understand, modify and retest?]
Portability [can I still use it even if I change the environment]

38. Hierarchical Models of Quality
Hierarchical Model of Boehm (1978)
Intermediate level characteristics – It identifies 7 quality factors that are expected by the software:
Portability
Reliability
Efficiency
Usability
Testability
Understandability
Flexibility
As-is Utility
Maintainability characteristics

39. Hierarchical Models of Quality
Hierarchical Model of Boehm (1978)
Primitive characteristics – Provides the foundation for defining quality metrics

40. Robustness / Integrity
Device Independence
Self-contained ness
Accuracy
Completeness
Robustness / Integrity
Consistency
Accountability
Device Efficiency
Accessibility
Communicativeness
Self descriptiveness
Structuredness
conciseness
Legibility
Augment ability
Portability
Reliability
Efficiency
Human Engineering
Testability
Understandability
Modifiability
Maintainability
As-is Utility
General Utility

41. Hierarchical Models of Quality
Summary of McCall & Boehm Models
Boehm’s and McCall’s models might appear very similar.
the difference is that:
McCall’s model primarily focuses on the precise measurement of the high-level characteristics “As-is utility”
Boehm’s quality model is based on a wider range of characteristics with an extended and detailed focus on primarily maintainability.

42. Hierarchical Models of Quality
Comparison of McCall & Boehm Models by QF to QF

43. Quality Measurement
Measurement of quality is one of the key problem highlighted by IT practitioners
Quality measurement is expressed in terms of Metrics that is a measurable property which is an indicator of one or more quality criteria that are seeking to measure
Conditions that the quality metric are:
It must be linked to the quality criterion that it seek to measure
It must be sensitive to different criterion
It provides determination of the criterion

44. Quality Measurement
Measurement technique to a software is similar to the traditional science methods. But it is more complex
“Structuredness” is the main factor for the software thro which quality can be measured.
Well structured code is easy to maintain & adapt which can be calculated in terms of average length of code modules in the program
Lines of code
Structuredness  modularity 
Number of modules

45. Quality Measurement Software Metrics
“Structuredness” is used to predict the maintainability, reliability & adaptability of the software later in the lifecycle
Classified into 2 types:
Predictive Metrics
Descriptive Metrics

46. Quality Measurement Software Metrics (Cont…)
Predictive Metrics – It is used to make predictions about the software later in the life cycle
Descriptive Metrics – It describes the state of the software at the time of the measurement
For Ex: reliability metric might be based upon the number of “system crashes” during the given period

47. Quality Measurements Gilb’s Approach
It is an iterative approach aiming to converge towards clear & measurable multidimensional objectives
This approach makes use the concept of McCall & Boehm models
For each stage, a partial product can be viewed with user where a product will be evaluated to identify whether it meets the needs of user. If it does not satisfy errors has to be identified & cleared out during the next iteration until a product gets satisfied by the user.

48. Quality Measurements Gilb’s Approach 5 problem areas highlighted
Simple fact that the method is different
Need of training & re-training and associated costs
Need of effective management
Need to measure progress towards the ultimate goal
Picking up errors

49. Quality Measurements Gilb’s Approach
With reference to Gilb’s approach, product quality can be measured in terms of “Quality Template”
It models quality in terms of Quality attributes & Resource attributes. This is because quality of a product can be constrained by the available resources

50. Quality Measurements Gilb’s Approach
“Quality Template” can be pictured as:
Workability
Availability
Adaptability
Usability
Other Qualities
People
Time
Money
Tools
Other Resources
Qualities
Resources

51. Quality Measurements Gilb’s Approach Quality Attributes Workability
Availability
Adaptability
Usability

52. Quality Measurements
Gilb’s Approach: Quality Attributes & its sub-attributes
Workability
Process Capacity
Storage Capacity
Responsiveness
Availability
Reliability
Maintainability
Integrity
Adaptability
Improvability
Extendability
Portability
Usability
Entry Level Requirements
Learning level requirements
Handling ability
Likability

53. Quality Measurements Gilb’s Approach: Quality Attributes Workability
It is defined as the ability of the system to do work (i.e., transaction processing)
Divided into sub-attributes of:
Process capacity – It is the ability of the system to process transactions with in a given unit of time
Storage capacity – It is the ability of the system to store information
Responsiveness – It is a measure of the response to a single event

54. Quality Measurements Gilb’s Approach: Quality Attributes Availability
It is the ability of the system to be used with the proportion of elapsed time
Classified into Sub attributes of:
Reliability
Maintainability
Integrity

55. Quality Measurements Gilb’s Approach: Quality Attributes Availability
Reliability
It is the ability of the system that should not fail from its operating environment under any circumstances
It is the degree to which the system does what it should to do.
Coz’ purpose of a system is different & the purpose of parts of a system will be different. So the assessment of reliability will also vary

56. Quality Measurements Gilb’s Approach: Quality Attributes Availability
Reliability
Based on the analysis of Dickson, Gilb’s have suggested that reliability can be assessed in terms of
Fidelity
Veracity
Viability
For both Logicware (code)
and Dataware (data files)

57. Quality Measurements Gilb’s Approach: Quality Attributes
Dickson’s classification of Reliability
Logicware
Fidelity
Concerned with the accuracy of algorithm implementation
Veracity
Concerned with the representation of “real world” be an algorithm
Viability
Is the extent to which an algorithm meets its specification in terms of performance & requirements
Dataware
Says how accurately an idea is represented by the data within a application
How well the data matches with the world
How well the required data fits the design constraints

58. Quality Measurements Gilb’s Approach: Quality Attributes Availability
Maintainability
It is the effort required to locate & fix a fault in the program within its operating environment
It is the process of fault handling
Sub-attributes of Maintainability are:
Problem recognition
Inspection Time
Administrative Delay
Active Correction
Tool Collection
Testing
Problem analysis
Test Evaluation
Correction
Recovery

59. Quality Measurements Gilb’s Approach: Quality Attributes Availability
Integrity
It is the protection of the program from unauthorized access
It is a measure of a system to remain intact under threat
Integrity may affects availability
So. A system with poor integrity is likely to be unavailable for much time

60. Quality Measurements Gilb’s Approach: Quality Attributes Adaptability
Classified into sub-attributes of:
Improvability – It is the time taken to make minor changes to the system
Extendability – It is the ease of adding new functionality to a system
Portability – It is the east of moving a system from one environment to another

61. Quality Measurements Gilb’s Approach: Quality Attributes Usability
It is the ability of the system that should facilitate the ease of use & effectiveness of a system
Classified into sub-attributes of:
Handling ability – It is a measure that says how well productivity can be proceeded after the error is detected
Entry level requirements – are human capabilities such as intelligence level, language proficiency
Learning level requirements – are resources such as time needed to reach the performance of the system
Likability – It says how well people like the system

62. Quality Measurements Gilb’s Approach: Resource Attributes People Time
Money
Tools
Other Resources

63. Quality Measurements Gilb’s Approach: Resource Attributes
Time Resource
2 types
Calendar time to delivery
Time taken by the system to carry out the task
People Resource
Measured in terms of “Man-years”
But the availability of People for the particular development is critical
Ex: can not utilize PASCAL programmers for C programming

64. Quality Measurements Gilb’s Approach: Resource Attributes
Money Resources
Concerned with both development & maintenance costs
In general, 80% of cost would be spent to maintenance for quality improvement
Tool Resources
It comprises all physical resources

65. Quality Measurements Gilb’s Approach: Resource Attributes
For continuous improvements, these resources will be considered as constraints to a product
People
Time
Money
Tools

66. Quality Measurements Gilb’s Approach: Resource Attributes
Gilb’s have defined some measures to quantify those attributes. And these can be measured in terms of “units per time”
For ex:
Transactions per second
Records per minute
Bytes per line
Bits per node per second

67. Quality Measurements Gilb’s Approach: Resource Attributes
Workability
Process Capacity
Units per time
Transactions per sec.
Storage Capacity
Units stored
Bytes per second
Responsiveness
Actions per time
Response time
Attribute Sub-attribute General measure Example

68. Quality Measurements GQM Model
GQM, the acronym for "Goal, Question, Metric”
It is an approach to “Software Metrics”
It was developed by Victor Basili of the University of Maryland & the Software Engineering Laboratory at the NASA Goddard Space Flight Center

69. Quality Measurements GQM defines a measurement model on three levels:
GQM Model
GQM defines a measurement model on three levels:
Conceptual level (goal)
A goal is defined for an object for a variety of reasons, with respect to various models of quality, from various points of view and relative to a particular environment.
Operational level (question)
A set of questions is used to define models of the object of study and then focuses on that object to characterize the assessment or achievement of a specific goal.
Quantitative level (metric)
A set of metrics, based on the models, is associated with every question in order to answer it in a measurable way.

70. Quality Measurements GQM Model
GQM templates are a structured way of specifying goals
Field
Examples
Object of study
pair programming, static analysis tool
Purpose
characterize, understand, evaluate, predict
Focus
programmer effort, program reliability
stakeholder
developer, customer, manager