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When looking at a requirement for a system behaviour that includes system performance, my understanding is that it is non-functional requirement, however, in some ways it is also considered functional requirement. I will share an example below

"The system must send an confirmation email after 5 seconds from the User Registration" This is a Non-Functional Requirement, because it involves performance that is measured by time

"The password expires after 60 days of inactivity" How come this is a functional requirement when it relates to the System Performance? If it deemed a business rule then the previous example is also a business rule, or am I missing something?

Many thanks for the advice

Hello. According to me:

1-Business rules are a kind of requirement. From them, we can derive system (product) requirements.

“Password expires after 60 days of inactivity” is a business rule. A derived system requirement could be: “the system shall reset the user’s password after 60 days of inactivity”.

2-Complete (functional) system requirements should be stated as follow:

[If Trigger-Event(s) occur [during Precondition(s),]] the system shall [not] perform Response-Action(s) [resulting in Postcondition(s) [within Quality-Threshold(s)]] (see D. Firesmith).

3-The distinction functional requirement vs non-functional requirement doesn’t really matter when elaborating the requirements. She makes sense later when designing and testing the system.

Hope having helped you,

Gildas

From my point of view, they are both business rules therefore Functional Requirements.