November 2003 J. B. Wordsworth: J3ISDQR4 1

Information Systems Development

Quality and Risk (4)

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What is a method?

• Defined way of performing an activity

• Defined inputs

• Notation for expressing outputs – syntax and semantics

• Heuristics – how to proceed

• Analysis approach

• Computational model

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Notation• Syntax – how to write it

– Java, VDM-SL, UML

• Semantics – what it means– Operational semantics of programming languages

• Worldliness – The world consists of objects (?)

• Relevance to the problem in hand– Java for programming, UML for recording a data

structure

• Formality– Z based on sets and logic; UML based on diagrams and

annotations.

November 2003 J. B. Wordsworth: J3ISDQR4 4

Heuristics

• Strength – how much guidance is given?– SSADM has strong heuristics.– VDM has weak heuristics.

• Correctness potential– Formal methods have high correctness

potential.– Object-oriented development has a weaker

correctness potential.

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Analysis approach

• Strength – degree to which we can check the quality of the outputs

• V&V potential – the degree to which we can verify or validate our outputs– Verification question – does the product agree

with its specification?– Validation question – does the product behave

the way its users expect?

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Computational model

• Specifies units of description and their relationships.– O-O uses objects with relationships of various

sorts.– CSP uses processes that synchronise on events

and pass information.

• There are lots of them – see next.

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Classification of methods

From Ould’s Managing Software Quality …

JSP, E-R model, UML class diagram

module hierarchy, JSD, UML interaction

diagram

ELH, VDM, Z, UML state diagram

Petri nets, CSP, CCS, UML activity

diagram

DFD, MASCOT, UML sequence

diagram

Petri nets, MASCOT, FSM, CCS, CSP, UML

state and activity diagram

data control

static

dynamic

event/time

place

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Choice of method

• Choose the view (dynamic, static, data, control).

• Choose the methods.– (Be prepared to use several.)

• Check the appropriateness of the computational model.

• Check the V&V potential.

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Quality achievement plan• Characterisation of system:

– data or control– concurrent operations– criticality

• Client expectations • Chosen development methods• Chosen tool support• Chosen target environment

– Development environment

• Consequent activities

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Verification opportunities

• Specifications– For consistency

– Against a standard

– Against a higher specification• For completenes

• For behavioural equivalence

• Code– Against a specification

– Against a standard

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Inspections

• Discovering defects in work products• Roles

– Moderator – Reader – Inspector

• Preparation• Meeting• Correcting the defects• Statistics

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Process Capability Maturity Model (CMM)

• Devised the by the SEI at Carnegie-Mellon University.

• Five maturity levels– Initial– Repeatable– Defined– Managed– Optimising

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Summary

• Methods help us perform the activities on the project plan.

• Methods contribute to product quality in various ways.

• There are many computational models to choose from.

• Quality control activities are an essential part of the project plan.