Ymris is the new Jena rules language, intended to supplement the existing language, provide support for new features such as aggregation and negation, and to allow scalable implementations for large RDF datasets. This is a preview release of Ymris, not a production release: some things don't work yet.
The introduction to Ymris explains and motivates the syntax and features of Ymris. The grammar is generated from the JavaCC used to construct the Ymris parser. If you want to explore the features of Ymris, see the interactive editor. Or you may be interested in using the Ymris reasoner in Jena code.
Comments on the preview should be directed to jena-devel@lists.sourceforge.net (note: not jena-dev).