I'm interested. My first question would be, "what kinds of real problems can I solve better/more easily/more expressively with UBL than with approaches we already have available?" That's the test that
UBL allows you to write Prolog-like code directly inside C++. The current Prolog is modeled directly to the Prolog standard. So IMHO your question is equivalent to "what kind of real problems can I solve better/more easily/more expressively with Prolog than with approaches we already have available in C++?" Prolog is the preferred language in the field of AI, expert systems, business logics, etc. There are lots of discussions about why Prolog is better in those areas than traditional procedure-oriented or object-oriented languages. I don't think that I can cover the reasons in just a few paragraph.