How exactly is meta-data organized within the files themselves? Are there generic categories setup within the data structure of a .wav, or can they be assigned manually, i.e. differently by each program that makes use of the files?

The reason for the question is that I'm currently embedding meta-data via PT, but I do have plans (eventually) to buy soundminer. I don't want to do all of this embedding now, only to turn around in 8 or 12 months time and have to re-do the entire thing because soundminer uses its own categorization system.