Curtis Dyreson, Michael Bvhlen, and Christian S. Jensen.
METAXPath
Journal of Digital Information. Also appears in Proceedings of the International Conference on Dublin Core and Metadata Applications (DC-2001), Tokyo, Japan, October 2001.
Journal Article
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Conference talk PPS

This paper presents the METAXPath data model and query language. METAXPath extends XPath with support for XML metadata. XPath is a specification language for locations in an XML document. It serves as the basis for XML query languages like XSLT and the XML Query Algebra.

The METAXPath data model is a nested XPath tree. Each level of metadata induces a new level of nesting. The data model separates metadata and data into different dataspaces, supports meta-metadata, and enables sharing of metadata common to a group of nodes without duplication. The METAXPath query language has a level shift operator to shift a query from a data level to a metadata level. METAXPath maximally reuses XPath hence the changes needed to support metadata are few. METAXPath is fully compatible with XPath.