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Design Quality

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Design Qualities

Design process needs high standards of quality

how much betterthe one is than the other??

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Contd

Quality cannot be measured in absolute Scale.- construction quality(How it is made?)- aesthetic value ( physical appearance)

- fit for purpose(comfortable, serves the purpose?)

Software

construction quality?- software is not manufactured

aesthetic value?

- most of the software is invisible- user interface (marginal concern)

fit for purpose?- Understand the purpose of customers

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Fitness for Purpose

Predicthow well the software will fit its purpose

Measure the relationship between software and itsapplication domain

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Assessing Design Quality

Objects are measured in terms of Physical Propertieslike length, weight, mass etc (ratio scales)

Ordinal scale elements can be ranked

measurement is concerned with capturinginformation about attributes of entities(Pfleeger,1997)

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Framework for Assessment

Quality concepts - abstract ideas about good andbad properties of a system.

Design attributes - provide a set of characteristics ofthe design entities (metrics).

Counts - realizing the design attributes

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Measuring Quality

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Fuller Mapping

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Contd

Use - identifies the purpose of making measurements.

quality factors - determine the quality concepts that

are associated with the purpose (ilities).

quality criteria - relate the requirements-orientedproperties of the intended system (the ilities) to the

solution-oriented properties of the design.

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Mapping from Quality Factors to Quality Criteria

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The Goal of fitness for purpose needed to recognizethe nature of the problem and its domain.

Efficiency- greater importance(embedded controlsystem)

Reliability Lesser importance than other factors

Aircraft autopilot - Lesser

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The ilities

The ilities form a group of quality factors - assessdesign quality.

Reliability

Efficiency

Maintainability

Usability

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Reliability

Designer predicts How the system works?

completeness - does it do everything it is supposed to do? (e.g.handle all possible inputs)

consistency- does it always behave as expected? (e.g.repeatability)

robustness - does it behave well under abnormal conditions?(e.g. resource failure)

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Efficiency & Maintainability

Efficiencyresources like processor time, memory, network

access, system facilities, disk space etc.

MaintainabilityHow easy will it be to modify in the future?

perfective, adaptive, corrective

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Usability

How easy is it to use?

user interface (HumanComputer Interaction, or HCI)

will form an important component

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Cognitive Dimensions framework

It gives design principles for notations, user interfacesand programming language design.

It provide a set of discussion tools - evaluating

quality concepts.

It provide a way in which some evaluation can be

done by the designers themselves

Thomas Green originally defined 14 cognitivedimensions

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