Well, with the ongoing developments to tabling this is changing. SWI-Prolog will in due time provide a modifiable set of facts and rules that provide well founded semantics for negation, guaranteed termination for a large class of programs (a superset of Datalog), automatic consistency maintenance and shared access from multiple threads.
Actually, most of that is working in the current git version as a proof of concept. Lots of work is still needed on robustness, user experience and scalability.
XSB is doing most of this stuff already single threaded and their facilities have some impact in the semantic web world for their reasoning facilities. SWI-Prolog has impact for threading, interfaces and being easy to use. Hopefully this will all be combined. With Web Prolog it can also be distributed over nodes