EXIF isn't really a standard, though it's supposed to be. There are areas for manufacturer's proprietary codes that generic EXIF readers may misinterpret, so very often things can look a bit odd.
If you use something like Canon's DPP software, the interpretation of the codes should make sense.
The actual technical specification is here -
http://www.exif.org/Exif2-2.PDF - but it's not a document you'll really want to try to read through!
You can try EXIFTOOL and EXIFREADER (both free programs) for extracting more from the EXIF data than Canon gives you with DPP