SWSL-Rules is a rule-based language, which can be used both as a specification and an implementation language for Semantic Web Services. SWSL-Rules is based on F-logic, HiLog, and Courteous Logic Programming.
(longer description if desired)
Relevance
This language incorporates many of the features that are deemed necessary for a RIF language. These include full Horn support, frames, higher-orderness, defaults.
Impact on Design
SWSL-Rules provides an example of a language design that incorporates many features that are important to RIF.
For More Information
http://www.w3.org/Submission/2005/SUBM-SWSF-SWSL-20050909/
RIFWG contacts: HaroldBoley, BenjaminGrosof, MichaelKifer, SaidTabet.