Software engineering

McCall’s Quality Factors Revision Adaptation Maintainability Flexibility Testability Portability Reusability Interoperability Operation The attributes that provide an indication of quality remain the same. Correctness The extent to which a program satisfies its specifications and fulfills the customer’s mission objectives Reliability The extent to which a program can be expected to perform its intended function with required precision. Efficiency The amount of computing resources required by a program to perform its function Integrity Extent to which access to software or data by unauthorized persons can be controlled. Usability Effort required to learn, operate, prepare input, and interpret output of a program Maintainability Effort required to locate and fix an error in a program Flexibility Effort required to modify an operational program Testability Effort required to test a program to ensure that it performs its intended function Portability Effort required to transfer the program from one hardware and/or software system environment to another. Reusability Extent to which a program can be reused in other applications Interoperability Effort required to couple one system to another. Correctness Reliability Usability Integrity Efficiency

Operation Correctness The extent to which a program satisfies its specifications and fulfills the customer’s mission objectives Reliability The extent to which a program can be expected to perform its intended function with required precision. Efficiency The amount of computing resources required by a program to perform its function

Operation Integrity Extent to which access to software or data by unauthorized persons can be controlled. Usability Effort required to learn, operate, prepare input, and interpret output of a program

Revision Maintainability Effort required to locate and fix an error in a program Flexibility Effort required to modify an operational program Testability Effort required to test a program to ensure that it performs its intended function

Adaptation Portability Effort required to transfer the program from one hardware and/or software system environment to another Reusability Extent to which a program can be reused in other applications Interoperability Effort required to couple one system to another

Measuring Quality Correctness Maintainability Integrity Usability

Measuring Correctness Degree to which software performs its function Defects/FP or Defects/KLOC Defects verify lack of conformance to requirements These are problems reported by the user after release Defects are counted over a standard period of time, typically during the first year of operation

Maintainability The ease with which a program can be corrected if an error is encountered, adapted if environment changes, enhanced if the customer requires an enhancement in functionality Its an ‘indirect measure’

Measuring Maintainability MMTC – mean time to change Time it takes to analyze the change request, design an appropriate modification, implement the change, test it, and implement it Spoilage – cost oriented metric The cost to correct defects encountered after the software has been released to the users

Integrity Software’s ability to withstand attack (both accidental and intentional) to its security. To measure integrity, two additional attributes are needed. threat security.

Integrity Threat is the probability (derived or measured from empirical evidence) that an attack of a specific type will occur within a given time Security is the probability that an attack of a specific type will be repelled. Integrity = Σ [(1-threat) x (1-security)]

Usability It is a measure of user friendliness Can be measured in terms of 4 characteristics: Physical or intellectual skill required learn the system The time required to become moderately efficient in the use of system The net increase in productivity A subjective assessment

Defect Removal Efficiency It’s the valuable at both the project and process level. Effectiveness of the quality processes during development as a percentage of total defects DRE = E/(E+D) E – errors found before delivery D – errors found after delivery (typically within the first year of operation)

Defect Removal Efficiency Capers Jones 1997 Sample Size – 1500 Projects