Why do you consider data storage as a non-functional requirement?

Data storage is considered a non-functional requirement because it describes properties of the system related to its quality and operation, rather than specific business logic.

Non-functional requirements define how the system should work, not what it should do. Data storage affects aspects such as:

• Reliability and fault tolerance
• Performance and access speed
• Scalability and availability
• Security and data protection

For example, a requirement like "data must be stored for at least 5 years" or "the system must provide backup" are non-functional requirements because they describe the quality and conditions of storage, not specific functions.

Thus, data storage is part of the system's infrastructure and operational characteristics, not a functional feature, and is therefore classified as a non-functional requirement.