Database Research Group

WSI – Database Systems Research Group


Pathfinder: A Purely Relational XQuery Processor

We believe that relational databases are the most researched and best engineered query processing infrastructures available today. They are able to efficiently query tons of data. By using a relational database as runtime environment for an XQuery processor we can port 30+ years of research to the XQuery domain and build a processor that is able to scale well with increasing input sizes.

Pathfinder is a re-targetable query compiler that turns XQuery expressions into table algebra queries. While Pathfinder is tightly coupled with MonetDB we also provide a SQL code generator that allows any database to become a faithful XQuery processor.

Pathfinder Overview

The Approach

Pathfinder assumes a database to store shredded XML documents—documents that are transformed into a relational encoding. An incoming XQuery query is compiled by Pathfinder into a relational query plan. The database evaluates the generated query plan based on the shredded XML documents and returns a table. A serializer consumes this table and transforms it into an XQuery result sequence. (In MonetDB/XQuery automatic shredding and serialization as well as the tight integration of Pathfinder lead to a runtime where the relational approach is not visible for the user anymore.).


Pathfinder has been released in the form of MonetDB/XQuery and is available at the MonetDB project. Note, though, that MonetDB/XQuery is no longer maintained and is only available in MonetDB releases up to March, 2011.