what is use of Classfactory , MapEnumerator and RunBase Class

i want to know what is use of class facory and mapEnumerator and Runbase class in Ax 2009

ClassFactory is used primarily for creating class instance - see all create*() methods, e.g. createClass(), formRunClass() etc. It also contains some related helper methods. Especially if you want to create a FormRun/ReporrtRun instance, you should always use ClassFactory.

The remaining classes are documented on MSDN: