Having written a chunk of my phd in prolog and even a simplified implementation of one, I'm definitely a fan. At the same time, our startup (graphistry) works w/ teams needing to look at all sorts of graph data, including knowledge graphs like the topic here, and I'd be nervous about meeting the performance & scale needs with out-of-the-box prolog systems. Likewise, a lot of prolog's power comes from ideas like automatically backtracking search, and I can't imagine using that in most team environments.

Datalog solves most of that :) My read of the paper is their semantics largely reduces to datalog. The most interesting semantic exception is their bounded recursion, which suggests they're doing optimizations normal datalog wouldn't. Likewise, graph workloads often have weird phenomena to optimize for in terms of expected queries & data, where I'm guessing datalog might fit semantically but not how people would normally implement an engine. The PathQuery paper carefully side-stepped all such discussion, so I've been curious.

At Graphistry, we do end-to-end GPU stuff, so I've been thinking about this particular problem, and came to a similar conclusion of a datalog-ish subset being the most straightforward way to get more performance/$ for this kind of task.