If you've got a big, complex application programming interface there are generally two ways to do it. You can assign an integer to each function (or method if it's an object-oriented interface) and share the mapping between integers and method names between the callee and caller, or you can provide a single function or method which takes a string.
The first way is generally used in older and more speed-sensitive code, since it has generally been a bit faster in the past (though for most purposes probably isn't significantly so now, especially for out-of-process calls - the context switch time will dwarf the string-lookup time).
The second way is used on the internet (where everything is text based and the network dominates most timings). It's also used in Windows DLLs (though this is more of a hybrid - the names are resolved to locations at DLL load time). COM, on the other hand, uses the first method (and has a lot of complicated registry/interface/type-library goo to make sure the numbers don't get out of sync).
I think that any time you have an API which is sufficiently complicated that it may change with future software or hardware releases, the string-based method is the way to go. Especially for something like this. Keeping track of all the possible variations of the mapping between method names and integers is always going to get sufficiently complicated that you might as well have the computer do it.