I have always thought that “descriptive” models says “what” but do not specify “how”, while “prescriptive” ones do exactly that. But when I started checking the topic, I found a lot of contradictions. Some say that process reference model in ISO 12207 is not prescriptive, while others say it is. As common examples of prescriptive models, the following are being named: waterfall, incremental, spiral… but to me it does not make sense, those are much more vague than the aforementioned ISO. CMM is said to be descriptive, yet to me it seems much more specific than e.g. the waterfall (I acknowledge these are dealing with different topic but I focus on the level of details).
he most common dispute I can find about ISO 9000. Some sources says it prescriptive, some say its descriptive.