Virtual eXist-db: Liberating Hierarchical Queries from the Shackles of Access Path Dependence

XQuery programs can be hard to write and port to new data collections because the path expressions in a query are dependent on the hierarchy of the data. We propose to demonstrate a system to liberate query writers from this dependence. A plug-and-play query contains a specification of what data the query needs in order to evaluate. We implemented virtual eXist-db to support plug-andplay XQuery queries. Our system adds a virtualDoc function that lets a programmer sketch the hierarchy needed by the query, which may well be different than what the data has, and logically (not physically) transforms the data (with information loss guarantees) to the hierarchy specified by the virtualDoc. The demonstration will consist of a sequence of XQuery queries using a virtual hierarchy, including queries suggested by the audience. We will also demonstrate a GUI tool to construct a virtual hierarchy.