Drools 2.0 Released "Drools is designed to allow pluggeable language implementations. Currently rules can be written in Java, Python and Groovy. Drools also enables Domain Specific Languages (DSL) via XML using a Schema defined for your problem domain. DSLs consist of XML elements and attributes that represent the problem domain. An XML Authoring tool provides a semi-rapid development environment with a drag and drop type interface based on the provided Schema."
Examples: House Example and Semantics Module Framework.
Searching around for a screenshot came across SEMANTIC CONFLICT DETECTION IN META-DATA – A RULE BASED APPROACH.