forgive me for sounding a little harsh, but you intend to build enterprise class software yet know very little about the subject matter you are going to be dealing with???
you need to go away and check out the potential competition and see what they do. I use OpenNMS at work, and it is superb... other points to mention along similar lines... how to classify them? well that's down to your design and your choices. if you need help have your own ideas in the first place i would be concerned.