Associated primarily with what the software does rather than how it does. Functionality is defined as the ability of the software product to provide functions which meet stated or implied needs of the user.
It refers to its capability to maintain its special level of performance under the specified conditions.
The usability of the software is primarily an external quality characteristic. It is a measure of effort needed to learn and use a software product for the purpose chosen. Three of its elements roughly correspond to it a typical line of software used: understandability, learnability, operability
Software efficiency deals with ying and yang elements of computation: space and time. Efficiency can be considered an indication of how well a system works, provided that the functionality requirements are met.
The maintainability of software is probably the clement that can best be approached at the levels of the software’s design and actual code. The capability to avoid unexpected effects from modifications to the software is also within the scope of this characteristic.
Portability refers to how easy it is to take the software for m one environment and transfer it to another. The main goal here is adaptability. This characteristic becomes particularly important in case of an application that is developed to run in a distributed heterogeneous environment of in a high performance computing platform, which lifespan is usually short.
Quality characteristics of software