Software Quality Management

Software Engineering Series Part 3

Definition of Quality

• Fitness of use - fidelity to requirements, available, reliable, accurate, speed and ease of use
• Absence of defects

Residual Defect Density

• Single measure of quality - Number of remaining defects per unit functionality
• Measured in two ways - Static RDD and Dynamic RDD
• Static RDD - Open defects per line of code; should interest the developer; Collected in Alpha tests
• Dynamic RDD - Open defects per transaction; detected at runtime; Collected in Beta tests and should interest the customers

Quality attributes

• Availability
• Reliability
• Accuracy
• Speed
• Ease of use

Availability

• How often is the system unavailable for use; either regularly or sporadically
• Planned and Unplanned downtime
• Defined in terms of planned hours of service, like between 7:00 AM to 10:00 PM and maximum allowable unplanned downtime, like not more than 15 minutes per working day.

Reliability

• How often does a system fail to perform a requested function or transaction
• Most system also specify the corrective actions to be taken in case of a failed transactions

Accuracy

• How often does the system give bad or wrong result
• Measure of how nearly correct is any information in the system. For example, the time of arrival of train in MRT station.

Speed/Performance

• How quickly can the system perform a transaction
• There are two aspects to speed - system performance (how fast the system can respond to a request) and ease of use (how easy or fast is the system for the user to make a request)

Ease of use

• How easy is the system to use from the users perspective
• Depends on many things such as system speed and accuracy, intuituveness, user speed and accuracy

Quality Specification

• Initial tasks of Quality management - specify (1) What is users expectation of quality (2) What quality is practically possible in the budget and timeline constraints (3) What is out of the scope
• All quality related specifications are referred in terms of metrics. Each quality attribute is measurable and is quantified and has a threshold value. This threshold value divides the acceptable from the unacceptable quality.
• Another important part of the specification is the mesaurability - how, when and by whom should the quality attribute measurements be taken.
• Finally the specification should lay in concrete terms the action plan - should specify the product components affected, checks or tests to be performed, roles and responsibilities of checkers and testers, actions to be taken in case of failures.

Verification Process

• Objective to prove to our satisfaction and the customer's satisfaction that the project output meets the requirements specification.
• Typically involves two parts - Quality Assurance and Quality Control and the various activities are carried out at several stages of the development phase.

Verification Techniques

• Inspection - Detailed and systematic scanning of the product by a skilled personnel; Generally done for documentation, help files, installation guides, navigation screens and other user centric components
• Reviews - Structured walkthrough of a product by a review team. Review team could be comprised of customers, development representative and perhaps an external expert; generally done for system architecture, high level design and workflow
• Tests - Black and White box testing; Stress test; generally dont for functional components

Verification Planning

• When - What points in life cyles
• What - system, functions, attributes
• Who - developer, customer, auditor
• How - process and technique
• Success criteria
• Follow up action

Final Verification

• Formal acceptance
• Notice of deviation
• Request for corrections
• Approval to continue
• Approval of payment

s

ss