What is software quality? What are McCall and ISO 9126 Quality factors?

To achieve a software of high quality is an ultimate goal. Software quality is assessed by internal and external quality criteria. External quality is critical to the user, while internal quality is meaningful to the developer only. Software quality is a mix of factors that vary across different applications and customers who request them.

McCall's Quality Factors
Software quality is affected by the factors that can be measured directly or indirectly. These include:
- During product operation, factors include correctness, reliability, usability, integrity and efficiency.
- During product transition, factors include portability, re-usability and inter-operability.
- During product revision, factors include maintainability, flexibility and test-ability.

ISO 9126 Quality Factors
This ISO was developed to identify quality attributes which includes:
- Functionality which includes the extent to which software is available for use indicated by sub attributes like suitability, accuracy, inter-operability, compliance and security.
- Reliability is amount of time software is available for use indicated by sub attributes like maturity, fault tolerance and recover-ability.
- Usability is the degree to which software is easy to use indicated by sub attributes like understand-ability, learn-ability and oper-ability.
- Efficiency is the extent to which software makes optimal use of resources indicated by sub attributes like time and resource behavior.
- Maintainability is an ease with which repair can be made to the software indicated by sub attributes like changeability, stability, testability.
- Portability is the ease with it can be transported from one environment to another indicated by sub attributes like adaptability, replace-ability.

What role does documentation plays in development process?

Documentation is a set of documents or informational products to describe a computer system. Each document is designed to represent particular function like reference, instructional and motivational.
Some types of documentation and informational products are system features and functions, user and management summaries, users manual, video and multimedia, tutorials, demonstrations, reference guide, technical references, system test models,
operations/operators manual, wall charts, newsletters.

A useful document furthers the understanding of the system's desired andactual behavior and structure. The criteria for measuring usability of documents are readability, availability, suitability and accessibility.

Purpose of Documentation

- It provides a reasonably permanent statement of a system's structure or behavior through reference manuals, user guides and systems architecture documents.
- It serves as transitory documents that are part of the infrastructure involved in running real projects.

Importance of Documents and Manuals

- Cost saving.
- They serve as sales and marketing tools.
- They serve as tangible deliverables.
- They serve as contractual obligations.
- They serve as security blankets.
- They serve as testing and implementation aids.
- They are used to compare the old and new systems.