If you have a C or C++ binding for your package system then you can use a compiled backend, which is more efficient than using helpers as described below. You can include the headers in the backend (with extra libraries) and then just write the simple code to interface with the methods of PackageKit. A C example can be found in backends/box and a C++ example in backends/apt.

You will have to use threading if your backend does not support async operation as requests have to return immediately. This is very important. Do any significant processing in a thread, and certainly don't return package results without creating a thread. By keeping the backends async we can make sure that there is no blocking which means the command line and UI do not freeze.