There is only one file type that uses the .XQ extension:
File written using XQuery, a language used for querying and manipulating data from XML data sources; contains source code that reads and extracts information using a logical data model created from an XML data source; used in various Web and desktop software products for handling XML content.
When reading data from a data source, XQuery operates at the logical data model level. Therefore, in addition to direct XML data sources, XQuery can be used for interpreting data from relational databases and object repositories. However, these other sources must include the appropriate middleware to present the source data as XML.
Updated: January 3, 2011