sdpm - lecture 8 - software quality assurance

Leiden Institute of Advanced Computer Science

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System’s Development and Project Management – Software quality assurance

Prof. dr. Thomas Bäck

Leiden Institute of Advanced Computer Science Dates

Feb. 1 14:45 – 17:30 Introduction, Project Description Feb. 2 13:45 – 16:30 STEP WISE Approach to Project Planning Feb. 9 13:10 – 15:45 STEP WISE Approach to Project Planning,

SAVE ENERGY Case Feb. 15 14:45 – 17:30 Selecting an Appropriate Software Dev.

Approach Feb. 16 15:15 – 18:00 Activity Planning and Resource Allocation Feb. 22 14:45 – 17:30 Software Effort Estimation Feb. 23 13:15 – 15:45 Risk management, project escalation Mar. 1 14:45 – 17:00 Exam Mar. 2 13:45 – 16:30 Risk Management, Project monitoring and

control Mar. 8 14:45 – 17:30 Software Quality Assurance Mar. 9 13:45 – 16:30 Managing People; Contract Management Mar. 18 15:00 – 17:00 Trade Fair

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STEP WISE overview

9. Execute plan

10. Lower level planning

0.Select project

1. Identify

project objectives 2. Identify project

infrastructure

3. Analyze pr. characteristics

4. Identify products and activities

5. Estimate effort for activity

8. Review/ publicize plan

6. Identify activity risks

7. Allocate resources

Review Lower level detail For each

activity

Some relate to qualities

Installation standards, procedures.

Special quality requirements ?

Entry, exit, process requirements ?

Review of overall quality aspects.


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Software quality

!  Of increasing concern !   E.g. safety critical systems, dependence on core

IS !  Project control concerns:

!   Need to make project progress visible !   Every task has a deliverable !   Errors accumulate with each stage !   Errors become more expensive to remove the

later they are found !   It is difficult to control the error removal process

(e.g. testing)


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Software quality

!  Three Specifications: !   Functional: What the system is to do. !   Quality: How well the functions are to operate. !   Resource: How much is to be spend on the system.


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ISO 9126 software qualities

Functionality Does it satisfy user needs?

Reliability Can the software maintain its level of performance?

Usability How easy is it to use?

Efficiency Relates to the physical resources used during execution

Maintainability Relates to the effort needed to make changes to the software

Portability How easy can it be moved to a new environment?


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ISO 9216

!  Defined in 1991 !  To tackle the question of definition of software

quality !  Also suggests sub-characteristics of the main

ones outlined here (outside main standard) !  See next slides


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Functionality sub-characteristics

!   Suitability !   Accuracy !   Interoperability

!   Ability of software to interact with other software components

!   Compliance !   Degree to which software adheres to application-related

standards or legal requirements, e.g. audit

!   Security !   Control of access to the system


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Reliability sub-characteristics

!  Maturity !   Frequency of failure due to faults - the more the

software has been used, the more faults will have been uncovered and removed

!  Fault-tolerance !  Recoverability

!   Note that this is distinguished from ‘security’ - see above


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Further quality sub-characteristics

!   Usability sub-characteristics: !   Understandability: easy to understand? !   Learnability: easy to learn? !   Operability: easy to use?

!   Efficiency sub-characteristics: !   Time behavior, e.g. response time !   Resource behavior, e.g. memory usage


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Further quality sub-characteristics (cont‘d) !   Maintainability sub-characteristics:

!   Analyzability: ease with which the cause of a failure can be found

!   Changeability: how easy is software to change? !   Stability: low risk of modification having

unexpected effects !   Testability


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Quality sub-characteristics (cont‘d)

!  Portability sub-characteristics: !   Adaptability !   Installability !   Conformance: standards that have bearing on

portability (compare to ‘compliance’) - e.g. use of high-level language

!   Replaceability: factors giving ‘upwards’ compatibility - ‘downwards’ compatibility is excluded


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Quality relationships

!   Indifferent !   One has no effect on the other

!  Competitive !   A system can only be good in respect to one

quality at the expense of another !  Complementary

!   A system which is good in respect to one quality is likely to be also good in respect to the other


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External qualities: !   Changeability

!   Testability

Internal vs. external qualities

Internal qualities (SQCs): !   Modularity !   Generality !   Expandability !   Self-descriptiveness

!   Simplicity !   Modularity !   Instrumentation !   Self-descriptiveness

Translate into


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External qualities: !   Portability

Internal vs. external qualities (cont’d)

Internal qualities (SQCs): !   Modularity !   Self-descriptiveness !   Machine independence !   Software system

independence


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Using ISO 9126 quality standards

!   Judge the importance of each quality for the application !   E.g. safety critical systems - reliability very

important !   Real-time systems - efficiency important

!  Work out ways of measuring quality !   E.g. mean-time between failures for reliability !   Response-time for efficiency


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!   Map measurement onto ratings scale to show degree of satisfaction:

Response (sec.)

Ratings (0-‐5)

<2 5

2-‐5 4

6-‐10 3

11-‐15 2

16-‐20 1

>20 0

Using ISO 9126 quality standards (cont’d)


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Quality Importance (a) Rating (b) Score (a x b)

Reliability 5 3 15

Efficiency 2 5 10

Usability 4 4 16

Total 41

Using ISO 9126 quality standards (cont’d)

!   Work out how ratings are to be combined !   ISO 9126 does not specify how to do that – only that

some method must be devised


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Software measurement

!  May apply to: !   Final products !   Intermediate products (predictive metrics)

!  May be: !   Relative or binary (does it/does it not exist?) !   Direct or indirect !   Tightly or loosely coupled


Quality specification

!  Each project has three sets of requirements !   Functional requirements: what the system is to do !   Quality requirements: how well it is to do it !   Resource requirements: how much it is going to

cost


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Quality specification, e.g. ‘ease of installation’ !  Definition of attribute

!   The amount of effort needed to install the package for a new customer

!  Measurement scale !   Hours

!  How tested !   Time needed to install system at three different

sites


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!  Worst acceptable limit !   4 hours

!  Planned limit !   1 hours

!  Best achievable !   30 minutes

Quality specification, e.g. ‘ease of installation’ (cont’d)

Define these for ‘user-friendliness’!


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How do we achieve product quality?

!  The problem: quality attributes tend to be retrospectively measurable

!  Need to be able to examine processes by which product is created beforehand

!  The production process is a network of sub-processes

!  Output from one process forms the input to the next

!  Errors can enter the process at any stage


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Product vs. process quality management

!  Errors are more expensive to correct at later stages !   Need to rework more stages !   Later stages are more detailed and less able to

absorb change !  Barry Boehm

!   Error typically 10 times more expensive to correct at coding stage than at requirements stage

!   100 times more expensive at maintenance stage


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For each activity, define…

!  Entry requirements !   These have to be in place before an activity can

be started !   Example: ‘a comprehensive set of test data and

expected results be prepared and independently reviewed against the system requirement before program testing can commence’


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For each activity, define… (cont’d)

!   Implementation requirements !   These define how the process is to be conducted !   Example: ‘whenever an error is found and

corrected, all test runs must be completed, including those previously successfully passed’


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For each activity, define… (cont’d)

!  Exit requirements !   An activity will not be completed until these

requirements have been met !   Example: ‘the testing phase is finished only when

all tests have been run in succession with no outstanding errors’

!  Software quality plan !   These requirements may be laid down in site

standards, or a quality plan may be drawn up for a specific project


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Inspections – general principles

!  When a piece of work is completed, copies are distributed to co-workers

!  Time is spent individually going through the work noting defects

!  A meeting is held where the work is then discussed

!  A list of defects requiring re-work is produced


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Inspections – advantages of approach

!  An effective way of removing superficial errors from a piece of software

!  Motivates the software developer to produce better structured and self-descriptive code

!  Spreads good programming practice !  Enhances team-spirit !  The main problem maintaining the

commitment of participants


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General movement to give software more quality !   Increase the visibility of software !  Put method into processes of development !  Check intermediate stages


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External standards – ISO 9001:2000

!   Ensure that a monitoring and control system to check quality is in place

!   Only certification of development process !   Not software development-specific !   Main activities:

!   Determine customer needs and expectation !   Establish quality policy !   Design product creation process with responsibilities !   Measure effectiveness and efficiency !   Take corrective action


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ISO 9001:2000 (Criticism)

!  Expensive, time consuming !  Putting smaller firms at a disadvantage !  Preoccupation with certification !  Can distract attention from real problems of

producing quality products


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External standards – Capability Maturity Model !  Levels of Process Maturity:

!   Level 1 – Initial: haphazard procedures followed •  Any organization at this level by default …

!   Level 2 – Repeatable: basic project management procedures

•  The way individual tasks are carried out will depend largely on person doing it.


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External standards – Capability Maturity Model !  Levels of Process Maturity:

!   Level 3 – Defined: how should each task in the softw. Development life cycle be done

!   Level 4 – Managed: products and processes are subject to measurement and control

!   Level 5 – Optimizing: improvements based on measurement data


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External standards – Capability Maturity Model (cont’d)

Level Key Process Areas

Initial Not applicable

Repeatable Configuration management, quality assurance, project planning, etc.

Defined Peer reviews, integrated software management, training program, etc.

Managed Quality management, process measurement and analysis

Optimizing Process change management, technology innovation, defect prevention

Software Configs, i.e., Version Control


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Summary

!   Quality = vague concept. Requirements have to be carefully defined.

!   There have to be practical ways to test relative presence / absence of a quality.

!   Most qualities can only be tested when system is completed.

!   We need ways of checking during development. !   Some procedures focus on testing products, others on

evaluating quality of the development process.

sdpm - lecture 8 - software quality assurance

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