I have seen content from various style guides and UX guidelines about this, and was wondering if there is a much more simple system to create a consistent and easy to implement design for various types of communication that occurs between users and systems. My initial idea is to use a Importance/Urgency matrix and assign different weightings to each combination. For example, Importance can be ranked High, Medium and Low, and Urgency can be ranked Immediate, Intermediate and Later. Has anyone seen this type of classification being used for Error, Warning, Status, Alerts and other types of messaging and notification or can provide some other approaches?

It looks like I should be looking at Impact (rather than importance) and Urgency, and use these to create priority. So are there good ways to grade or classify each of these categories?