System requirements are features and functionalities that are used to create a software solution in practice. They can be functional and non-functional.
Understanding the differences between functional and non-functional requirements helps deeply analyze project needs and identify the proper scope of work. Besides, knowing the differences will empower you to support users with a better experience and satisfy the stakeholders with their needs and requirements.
When talking about functional requirements, we usually think along the lines of what the system should do.
We expect the functional requirements to deal with the following questions:
- What are the business flows of the system? For example, login, storing photos, or more.
- What business services should the system have? For example, logging service, data access service, or more.
- What does the user interface of the system looks like? For example, look and feel, general guidance, responsiveness, and more.
You can identify those requirements from answering those questions of what the system should do.
Non-functional requirements basically describe what is expected environment for the system with emphasis on edge cases.
The non-functional requirements answer roughly this question of what the system should deal with.
The most common non-functional requirements are:
- Data Volume
- Concurrent Users
- SLA (Service Level Agreement)
Functional vs Non-Functional Requirements
|Functional Requirements||Non-Functional Requirements|
|Key Question||What should the system do?||What should the system deal with?|
How should the system perform the tasks?
|Result||Product features||Product properties|
|Focus||User requirements||User expectation and experiences|
|Property||Use cases||Quality attributes|
|Role||System functionality||System performance|
|Identification Difficulty||Quite evident to define||Quite hard to discover, unobvious|