On the tradeoff between mapping and querying power in XML data exchange
Shunichi Amano, Claire David, Leonid O. Libkin, Filip Murlak · 2010
In XML data exchange, a schema mapping specifies rules for restructuring a source document under the target schema, and queries over the target document must be answered in a way consistent with the source information. Mapping rules and queries in this scenario are typically based on various kinds of tree patterns. Patterns with downward navigation have been studied, and tractable classes of mappings and queries have been isolated.