Querying XML Data: As You Shape It

A limitation of XQuery is that a programmer has to be familiar with the shape of the data to query it effectively. And if that shape changes, or if the shape is other than what the programmer expects, the query may fail. One way to avoid this limitation is to transform the data into a desired shape. A data transformation is a rearrangement of data into a new shape. In this paper, we present the semantics and implementation of XMorph 2.0, a shape-polymorphic data transformation language for XML. An XMorph program can act as a query guard. The guard both transforms data to the shape needed by the query and determines whether and how the transformation potentially loses information, a transformation that loses information may lead to a query yielding an inaccurate result. This paper describes how to use XMorph as a query guard, gives a formal semantics for shape-to-shape transformations, documents how XMorph determines how a transformation potentially loses information, and describes the XMorph implementation.