Boehm's Quality Model

      This model was introduced in 1978, it is very similar to McCall quality Model as it is also represents a hierarchical quality model which includes high-level characteristics, mid-level characteristics and primitive characteristics. 

      The high-level characteristics explains around how the elevation of software quality could be put. Here the three main things needs to be taken care of:

1. Usability
2. Maintainability
3. Portability

       The Mid-level characteristics represents the Boehm's 7 quality factors which are the most important qualities to be expected from a software:

1. Portability- The code possesses the capabilities of operating easily and well on a system configuration other than the current one.
2. Reliability- The code possesses the capabilities of performing the given functions or task successfully in case of any system crash or failure.
3. Efficiency- The code possesses the capabilities of fulfilling its purpose without any waste of resources.
4. Usability- Code possesses the characteristic usability to the extent that it is reliable, efficient and human-engineered.
5. Testability- The code supports the establishment of verification criteria and evaluation of its performance.
6. Understandability- The code possesses the characteristics as the purpose of the code is clear to the inspector.
7. Flexibility- the ease of changing the software to meet revised requirements.

        The lowest level structure of the characteristics hierarchy is the primitive characteristics metrics hierarchy.

        There are many factors responsible for following such models, like accuracy, consistency, robustness, accessibility, efficiency, device independence, completeness, accountability, communication, detailed understanding, legibility, structuredness, Augmentability, conciseness.

        Though Boehm’s and McCall’s models might appear very similar, the difference is that McCall’s model primarily focuses on the precise measurement of the high-level characteristics “As-is utility”, whereas Boehm’s quality model is based on a wider range of characteristics with an extended and detailed focus on primarily maintainability.

        This model is an improvised version of McCall's model and as the Boehm's model is placed in hierarchical order it is used in a widespread manner. Even after having overcoming the problems of McCall's model still it hands a very minute support because of the top down approach to see quality of software, Boehm's model can't be followed always for a top notch software quality.