First we need to define each one:
An example of a functional requirement would be:
- A system must send an email whenever a certain condition is met (e.g. an order is placed, a customer signs up, etc).
A related non-functional requirement for the system may be:
- Emails should be sent with a latency of no greater than 12 hours from such an activity.
now we talk about the diferences between them:
In other words, a functional requirement will describe a particular behaviour of function of the system when certain conditions are met, for example: “Send email when a new customer signs up” or “Open a new account”.
A functional requirement for an everyday object like a cup would be: “ability to contain tea or coffee without leaking”.
Typical functional requirements include:
- Business Rules
- Transaction corrections, adjustments and cancellations
- Administrative functions
- Authentication
- Authorization levels
- Audit Tracking
- External Interfaces
- Certification Requirements
- Reporting Requirements
- Historical Data
- Legal or Regulatory Requirements
In other words, a non-functional requirement will describe how a system should behave and what limits there are on its functionality.
Non-functional requirements generally specify the system’s quality attributes or characteristics, for example: “Modified data in a database should be updated for all users accessing it within 2 seconds.”
A non-functional requirement for the cup mentioned previously would be: “contain hot liquid without heating up to more than 45 °C”.
Typical non-functional requirements include:
- Performance – for example: response time, throughput, utilization, static volumetric
- Scalability
- Capacity
- Availability
- Reliability
- Recoverability
- Maintainability
- Serviceability
- Security
- Regulatory
- Manageability
- Environmental
- Data Integrity
- Usability
- Interoperability
