Software Engineering Lec#9

Non-functional requirements
It is define system properties and constraints e.g. performance, security, availability, reliability, response time and storage requirements. Constraints are I/O device capability, the data representations used in system interfaces. Non-functional requirements may be more critical than functional requirements. If these are not met, the system may be useless. Non-functional requirements usually specify the system as a whole.
Although it is often possible to identify which system components implement specific functional requirements, it is often more difficult to relate components to non-functional requirements. The implementation of these requirements may be diffused تنتشر throughout the system. There are two reasons for this:
? Non-functional requirements may affect تؤثر ب the overall architecture of a system rather than the individual components. For example, to ensure that performance requirements are met, the evaluator may have to organize the system to minimize communications between components.
? A single non-functional requirement, such as a security requirement, may generate a number of related functional requirements that define system services that are required. In addition, it may also generate requirements that restrict existing requirements.
Non-functional requirements arise through user needs, because of budget constraints, organizational policies, the need for interoperability with other software or hardware systems, or external factors such as safety regulations or privacy legislation تشريع . The next figure shows a classification of non-functional requirements.