Subsumption for XML types

XML data is often used validated stored queried etc with respect to di erent types Understanding the relationship between these types can provide important information for manipulating this data We propose a notion of subsumption for XML to capture such relation ships Subsumption relies on a syntactic mapping between types and can be used for facilitating validation and query processing We study the properties of subsumption in particular the notion of the greatest lower bound of two schemas and show how this can be used as a guide for selecting a storage structure While less powerful than inclusion sub sumption generalizes several other mechanisms for reusing types notably extension and re nement from XML Schema and subtyping