XPCE is the so-called Prolog graphic library , although it isn't Prolog at all. Like they mention in it's manual, XPCE is not Prolog; XPCE is an object-oriented language that has absolutely nothing to do with Prolog.
The first thing that we need to do to create applications in XPCE is to install Swi-Prolog. You can find it at it's distributor page.
The page about XPCE is http://www.swi-prolog.org/packages/xpce/.
to be continued...