usability - How to define/classify messages and notifications in web applications

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? And how can these be linked to specific look & feel so they can be easily implemented by the front end developers?

Update

Looking at some of the front-end development framework these days, there has been some need to classify messages and notifications due to the CSS applied to HTML elements. An example from Foundation 5.0

And Bootstrap 3.0

To clarify the question a bit further, I am trying to look at it from the user's perspective in terms of what types of messaging that they would expect to see and what the behaviours should be like (in the context of web applications). The front-end development frameworks provide some idea about the style but doesn't make a strong link with the expected behaviour. This is something that should be independent of business rules because we are talking about a system or scheme that can be used to describe and categorize the messages and notifications consistently.

Answer

(I edited the answer for the sake of clarity)

Re-reading your question, it seems you are more after a way to classify messages in categories like Status, Warning and Error. To me those cannot be classified automatically, because knowledge of the business case is necessary to do so. You can maintain a matrix of classification that you will enrich over time.

I add below some information about Event Management and Incident Management, which are part of ITIL, and could be of some use for your particular case.

---

Priority is usually considered as a function of impact and urgency. Information, warning and exceptions are levels of information, generated by events.

ITIL has a matrix that describes priority depending on impact/urgency.

ITIL suggests that priority be made dependent on Impact and Urgency. Out-of-box, this is true on incident forms. Priority is generated from Urgency and Impact according to the following table:

           Urgency 1   Urgency 2   Urgency 3
Impact 1   Priority 1  Priority 2  Priority 3
Impact 2   Priority 2  Priority 3  Priority 4
Impact 3   Priority 3  Priority 4  Priority 5

(Source: http://wiki.servicenow.com/index.php?title=ITIL_Incident_Management)

I am adding more information, from the comments i've received it's not clear for everyone how you get the urgency and the impact in the first place.

What is important to note is that the classification of impact/urgency depends of your organization and business case.

Urgency categorization example

Category   Description
High (H)   The damage caused by the Incident increases rapidly.
           Work that cannot be completed by staff is highly time sensitive.

           A minor Incident can be prevented from becoming a major Incident by acting immediately.
           Several users with VIP status are affected.
Medium (M) The damage caused by the Incident increases considerably over time.
           A single user with VIP status is affected.
Low (L)    The damage caused by the Incident only marginally increases over time.
           Work that cannot be completed by staff is not time sensitive.

(Source: http://wiki.en.it-processmaps.com/index.php/Checklist_Incident_Priority)

Considering the different event types, ITIL describes 3 categories: Information, Warning, and Exception.

Informational events are typically events within normal operating boundaries. They are the types of “good” events that tend to fill most IT Service Management tools. These events are typically an indication that something has worked as it should.

Warnings are an early indicator or potential indicator of trouble. However, we need to understand that a warning is a flag to something being “unusual”, not necessarily negative (e.g. someone logs in after 6 weeks of inactivity)

Exceptions are the most typical precursor to incidents, but they will not always lead to an incident (e.g. a CPU spikes above the set threshold as a power user starts a processing job). Exception events will generally be of interest to IT Operations staff as they may be a sign of more trouble to come.

(Source: http://itsm.certification.info/event2.html)

One thing to note is that event management and incident management are linked, but not completely. You can have incidents (so impact/urgency giving you a priority) without having an event of the form information/warning/exception (for example if a user calls to say something is not working, compared to when your monitoring would throw an exception because a service is down).