Every software system are classified as functional or non-functional requirements.
Functional statement mean what the system actually do or we can say how the system will act when an input will be entered or how the system will behave in particular situation.
Functional requirement simply describes about the system what function or activities are performed by the system. Most of the time these requirements are depends on the particular nature of the system and expected end users of the software.
When we are writing the user requirements, we will write down the requirements in general language which is easily understandable by the managers and end users of the software. When we are writing the requirement for the developers and system professionals, we will use particular system functionalities and their inputs and outputs in specific technical languages.
Every system has some special constraints which helps to perform the system services in efficient way. System constraints like, timing constraints, standards and development constraints.
Non Functional requirements are not directly linked with the services performed by the system or end users of the system, but non-functional requirements are constraints or characteristics of the system as whole. Most of the time the end user may find the way to work in the absence of a functional requirement, but in the absence of a non-functional requirement the whole system is unusable to perform the specific tasks.
|Speed||Transactions or actions performed per second
Response to the user or event or we can say the page or screen refresh time.
|Availability||Mean the availability of the software of system to the end users.|
|Security||How secure the user personal data and credentials are.|
|Usability||The way a user can understand the system and operate the system without a serious efforts.|