The DMTF has instituted strict rules regarding the way a model may change between versions and version numbers in the form major. minor. update (e.g., 2.7.1) have been added to all classes. Releases where the major release number does not change (e.g., between version 2.7.2 and 2.8.1) are known as "point releases." Releases where the major version number changes are known as "major releases."
For point releases, a number of backward compatibilities are guaranteed and a formal process is used to make changes to the model.
Assume it was decided that introducing a CIM_Toaster class into the device common model in a previous version had been a bad idea. Simply removing it might break programs already running in products and so it would first have the DEPRECATED qualifier attached to it, if possible pointing the programmer to the class which should be used instead. By deprecating the class in this way, its use is discouraged, but programs already using it continue to work.
Adding a new class to the model is a simpler problem because maintaining compatibility with earlier releases is not an issue. Although a version of the model is in flux and discussions are in progress within the DMTF, the new class will have the EXPERIMENTAL qualifier added to it. This discourages engineers from making use of a class which may disappear before the formal point release. Once the discussion is over and the point release is ready, the EXPERIMENTAL qualifiers disappear.
Major releases provide the DMTF with the opportunity to clean up all the deprecated classes and properties. Of course, this breaks backward compatibility by removing classes on which programs may be relying. To date there has been no major release and the precise mechanism is undecided and unproven.