A trace semantics for positive core XPath

We provide a novel trace semantics for positive core XPath that exposes all intermediate nodes visited by the query engine. This enables a detailed analysis of all information relevant to the query. We give two examples of such analyses in the form of access control policies. We translate positive core XPath into linear temporal logic, showing that branching structures can be linearised effectively. We use the SPIN model checker in a proof of concept implementation to resolve the queries, and to perform access control. The performance of the implementation is competitive.