system upgrade, ehp - funcionalities

Where can I find which funcionality upgrade is done by which enhacement package (ehp 4...) and with release levels (4.7, 5.0, 6.0)? For exmaple what is diff in funcionalities between 4.7, 5.0 and 6.0, and e.g. ehp4 which new funcionalities have?

Thanx

Maya