Using a relational processor and an XPath processor to evaluate joint queries
Royi Ronen, Oded Shmueli · 2008
Conjunctive queries (CQs) are a common abstraction for many query languages (or significant parts thereof) for relational data, XML data or both, such as SQL, XPath, XQuery, XSLT and SQL4X. This work considers the joint querying of relational and XML data by adding an XPath predicate to the CQ formalism. CQs are a basic building block of query processing understanding, and in that respect, adding an XPath predicate is a natural extension. Relational and XML data are "connected" either via references to XML nodes that are stored in relations (essentially oids, usually the result of previous queries) or via atomic text values. Then, relational and XML data are jointly referenced by allowing variables to be shared by relational and XPath predicates.