Two Towers by Ora Lassilla points out a paper Semantic Web Architecture: Stack or Two Towers?
(PDF) by Horrocks, Parsia, Patel-Schneider and Hendler (not clear where it's published) that reviews the current semantic web architecture state and argues that there is an emerging clash of two stacks of semantics, one DLP-Datalog, Datalog rules stack incompatible with the RDF / OWL / First Order Logic extensions of OWL semantic web stack, leaving the only option for it to start again from raw XML.
Seems like going backwards to me but maybe somebody who understands this area better will explain it to me in small words!