2.2 Why Non-Functionality is so Important?

The lack of non-functional issues in software components has some negative effects on many software development tasks.

• Specification. Non-functional characteristics of software remain hidden to the user and they only appear in (optional and informal) software documentation. Their absence leads to an unbalanced specification, where functional aspects are well covered with usual specification languages while non-functional ones do not exist.
• Implementation. The selection and/or development of the most appropriate (with respect to non-functional requirements) implementation for software modules cannot be assisted at all because of lack of information. As a result, the decisions to be taken during this process may be difficult and even incorrect.
• Maintenance. Changes in the system environment, modifications of existing software module implementations, and creation of new implementations require a new (by-hand) review of previously taken implementation decisions, without having available the non-functional information of the system, which is affected by these changes [FB97].
• Reusability. Software reuse cannot take non-functional issues into account. Thus, components selected by any functional-oriented reuse strategy may not fit into the non-functional requirements of the environment, hindering or even preventing their actual integration into the system.