Your background data helps clarify your perspective, and your point is valid. I’m still in more of the “make sense of the mess” mode than “try and force changes to fix it” mode. Maybe that will change.

Either way, thanks very much for helping create a community here and for keeping the discussion going on the stuff you are passionate about!

1. The classical gurus, such as Donald Gause and Gerald Weinberg, put forth a coherent vocabulary for requirements concepts. They were not always perfectly consistent, but the inconsistencies were minor.

2. Confused people, heavyweight methodologies, and Conway’s Law distorted and expanded the classical vocabulary in a manner that produced glaring inconsistencies and incoherence (e.g. “functional requirements specifications” that contain nonfunctional requirements).

3. Folks like Karl Weigers attempted to account for all of the diverse terminologies but didn’t point out their flaws.

Merely noting and accounting for the terminology that’s out there is fine. But in your diagrams and posts, you’ve portrayed the terminology – at least implicitly – as consistent and coherent. I don’t think it’s proper to portray the notion of a requirement that describes what the product should do yet isn’t functional in that manner.

1. Market requirements are neither functional nor nonfunctional. The distinction simply doesn’t apply to market requirements.
2. Similarly, product requirements are neither functional nor nonfunctional.
3. The document that some call an FRS (functional requirements specification) contains (or at least should contain) nonfunctional requirements and is therefore a misnomer.

Now, let’s examine an example you have given of a product requirement:

“The system shall recommend ingredient purchase amounts and timing that would reduce spoilage by at least 50% against the baseline.”

Since this statement specifies a product requirement, you would consider it neither functional nor nonfunctional. But it is equivalent to the combination of two requirements:

R1. The system shall recommend ingredient purchase amounts and timing.
R2. Spoilage stemming from the system’s purchase recommendations shall not exceed 50% of the baseline amount.

R1 specifies what the system should do. R2 specifies a measurable, characterizing aspect of R1.

In light of this analysis, why do you not consider your example of a product requirement a combination of a functional and nonfunctional requirement?