Most examples of bundle identifiers have three parts. Are four part bundle identifiers valid in iOS? How about n-part? (n > 3)
com.companyname.divisionname.appname
[1st name].[2nd name]...[n-1th name].[nth name]
There is no limit I know of. I personally used bundleIDs with up to 6 parts, they all passed verification and now live happily in the App Store.