Xcerpt can be used for querying, possibly in a same query program, both XML and RDF resources.
Xcerpt's rule-based queries are an example of rules that might be interchanged on the Web.
Impact on Design
Xcerpt suggests an approach to integrating query languages in a Rule Interchange Format.
For More Information
An extension of Xcerpt, called XChange, is a language of Event-Condition-Action rules for reactivity on the Web.