McCall identified 11 factors in 1978 that can be used to develop software quality metrics by measuring attributes of a software product during its operation, revisions, and transitions between environments. The factors relate to correctness, reliability, efficiency, integrity, usability during operation, and maintainability, flexibility, and testability during revisions. Additional factors include portability, reusability, and interoperability. Measuring these factors allows the quality of software that is in use to be inferred based on observable attributes.

1. Software Quality
Factor

2. Software Quality Factor
 In 1978, McCall identified factors that could be used to develop metrics for
the software quality. These factors try to assess the inner quality of
software from factors that can be observed from outside. The basic idea is
that the quality of the software can be inferred if we measure certain
attributes once the product is put to actual use. Once completed and
implemented, it goes through three phases: operation (when it is used),
during revisions (when it goes through changes), and during transitions
(when it is ported to different environments and platforms).

3. During each one of these phases, different
types of data can be collected to measure the
quality of the product. McCall’s model is
depicted and explained as follows.

5. Factors related with 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
• 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

6. Factors related with 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

7. Types of Facter:
• Portability
– Effort required transferring 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.