[Newbie] GNU Prolog / C interface

Hello group!

I am a newbie to PROLOG, though we learnt some at school years ago
(using a DOS-based interpreter). Now I want to learn about more 'recent'
implementations, esp. GNU Prolog (I am running GNU/Linux on my PC).
The thing that thrills me most about gprolog is its C interface, as I
intend to use Prolog as a kind of "logic engine" within C and Pascal
programs.
I tried to figure out things with the official gprolog documentation,
but I don't seem to pick it up well from it. Is there any tutorial you
can recommend concerning ISO prolog and more specifically, for the GNU
Prolog C interface?

Thanks in advance
Tobias Guggenmoser