Software Quality Requirements and Factors-3

7/31/2019 Software Quality Requirements and Factors-3

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Software Quality

Factors


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The need for a comprehensiveThe need for a comprehensivesoftware quality requirementssoftware quality requirements

There are some characteristic common :All the software projects satisfactory fulfilled the basicrequirements for correct calculations

All the software projects suffered from poor performancein important areas such as maintenance, reliability,software reuse, or training.

The cause for the poor performance of the developedsoftware projects in these areas was the lack of predefinedrequirements to cover these important aspects of thesoftwares functionally .


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The need for a comprehensiveThe need for a comprehensivedefinition of requirementsdefinition of requirements (2)(2)

There is a need for a comprehensivedefinition of requirements that will cover allattributes of software and aspects of theusability aspects, reusability aspects,maintainability aspects, and so forth inorder to assure the full satisfaction of theusers.


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Classification of software requirementsClassification of software requirementsinto software quality factorsinto software quality factors

The classic model of software qualityfactors suggest by :

McCall (consist of 11 factors, 1977)Deutsch and Willis (consist of 12 to 15 factors,1988)Evans and Marciniak (1987)


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McCalls Factor ModelMcCalls Factor Model

Classifies all software requirement into 11software quality factors, grouped into threecategories :

1. Product operation factors : Correctness,Reliability, Efficiency, Integrity, Usability.2. Product revision factors : Maintainability,

Flexibility, Testability.3. Product transition factors : Portability,

Reusability, Interoperability.


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Product OperationProduct OperationFactorsFactors


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Product Operation : CorrectnessProduct Operation : Correctness

Correctness requirements are defined in a list of thesoftware systems required outputs.

Output specifications are usually multidimensional;some common dimensions include :

o The output missiono The required accuracy of outputo The completeness of the output information

o The up-to-dateness of the informationo The availability of the informationo The standards for coding and documenting the software

system.


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Product OperationProduct Operation -- ReliabilityReliability

Reliability requirements deal with failures to provide service.Determine the maximum allowed software system failuresrate, and can refer to the entire system or to one or more of its separate functions.

Examples :1. The failures frequency of a heart-monitoring unit that will operate in a

hospitals intensive care ward is required to be less than one in 20years. Its heart attack detection function is required to have a failurerate of less than one per million cases.

2. One requirement of the new software system to be installed in themain branch of Independence Bank, which operates 120 branches, isthat it will not fail, on average, more than 10 minutes per monthduring the banks office hours.


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Product OperationProduct Operation -- EfficiencyEfficiency

Efficiency requirements deal with the hardwareresources needed to perform all the functions of thesoftware system in conformance to all other requirements.

Examples :1. A chain stores is considering two alternative bids for a

software system.


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Product OperationProduct Operation -- IntegrityIntegrity

Integrity requirements deal with the softwaresystem security, that is requirements to presentaccess to an authorize person,[to distinguish between the majority of personnel allowed to see theinformation (read permit) and a limited group who will be allowed toadd and change data (write permit), and so forth.]

Example :GIS SW allowed citizens access to its GIS through Internet only for viewingand copying data but not to insert changes.


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Product OperationProduct Operation -- UsabilityUsabilityUsability requirements deal with the scope of staff resources

needed to train a new employee and to operate the softwaresystem .

Example :The software usability requirements document for the newhelp desk system initiated by a home appliance servicecompany lists the following specifications :

a. A staff member should be able to handle at least 60 servicecalls a day

b. Training a new employee will take no more than two days,immediately at the end of which the trainee will be able tohandle 45 service calls a day.


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Product RevisionProduct RevisionFactorsFactors


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Product Revision software QualityProduct Revision software QualityFactorsFactors

According to the McCall model of software qualityfactors, three quality factors comprise the productrevision category. These factors deal with those

requirements that affect the complete range of software maintenance activities :o Corrective maintenanceo Adaptive maintenanceo Perfective maintenance


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Product RevisionProduct Revision -- MaintabilityMaintabilityMaintainability requirements determine the efforts that will

be needed by users and maintenance personnel to identify thereasons for software failures, to correct the failures, and toverify the success of the corrections.

This factors requirements determine refer to the modular structure of software, the internal program documentation,and the programmers manual, among other items.

Example typical maintainability requirements :a. The size of a software module will not exceed 30 statements.b. The programming will adhere to the company coding standards

and guidelines.


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Product RevisionProduct Revision -- FlexibilityFlexibility

The capabilities and efforts required to supportadaptive maintenance activities are covered by theflexibility requirements.

These include the resources (in man-days) required toadapt a software package to a variety of customers of the same trade, of various extents of activities, of different ranges of products, and so on.

This factors requirements also support perfectivemaintenance activities.


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Product RevisionProduct Revision -- TestabilityTestability

Testability requirements deal with the testingof an information system as well as with itsoperation.

Testability requirements for the ease of testingare related to special features in the programs

that help the tester, for instance by providing predefined intermediate results and log files.


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Product TransitionProduct Transition

FactorsFactors


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Product TransitionProduct Transition -- PortabilityPortability

Portability requirements tend to theadaptation of software system to other environenments consisting of differenthardware, different operating systems, and soforth.


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Product TransitionProduct Transition -- ReusabilityReusability

Reusability requirements deal with theuse of software modules originallydesigned for one project currently beingdeveloped.


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Product TransitionProduct Transition --InteroperabilityInteroperability

Interoperability requirements focus oncreating interfaces with other software systems

or with other equipment firmware.Interoperability requirements can specify thename of the software or firmware for whichinterface is required.


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Alternative Models of SoftwareAlternative Models of SoftwareQuality FactorsQuality Factors

Formal comparison of the alternativemodels (Evans M 1987, Deutsch & Willis

1988)Comparison of the factors models-contentanalysis (verifiability, expandability, safety,

manageability, survivability)Structure of the alternative factor models


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Who is interested in the definitionWho is interested in the definitionof quality requirements?of quality requirements?

Some quality factors not included in the typicalclients requirements document may, in many cases,interest the developer.The following lists of quality factors usually interestthe developer whereas they may raise very littleinterest on the part of the client :

o Portability

o Reusabilityo Verifiability


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Requirements DocumentsRequirements Documents

A project will be carried out to according totwo requirements documents :

The clients requirements documentThe developers additional requirementsdocument


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Software Compliance withSoftware Compliance withQuality FactorsQuality Factors

The softwares product compliance to therequirements belonging to the various qualityfactors is measured by software quality metrics,measures that quantify the degree of compliance.In order to allow for valid measurements of compliance, sub-factors have been defined for

those quality factors that represent a wide rangeof attributes and aspects of software use.


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Factors and sub-factors


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Factors and sub-factors (cont.)


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Factors and sub-factors (cont.)


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Summary

1. The need for a comprehensive requirementsdocuments and their contents.2. The structure (categories and factors) of

McCalls classic factor model.3. The additional factors suggested by

alternatives factor models.

4. Those interested in defining software qualityrequirements.


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Questions ?

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Software Quality Requirements and Factors-3

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