Bry, François; Schaffert, Sebastian
The XML Query Language Xcerpt: Design Principles, Examples, and Semantics.
NODe 2002 Web- and Database-Related Workshops, 7. - 10. Oktober 2002, Erfurt, Deutschland.
Most query and transformation languages developed since the mid 90es for XML and semistructured data—e.g. XQuery , the precursors of XQuery , and XSLT —build upon a path-oriented node selection: A node in a data item is specified in terms of a root-to-node path in the manner of the file selection languages of operating systems. Constructs inspired from the regular expression constructs , +, ?, and “wildcards” give rise to a flexible node retrieval from incompletely specified data items.
This paper further introduces into Xcerpt, a query and transformation language further developing an alternative approach to querying XML and semistructured data first introduced with the language UnQL . A metaphor for this approach views queries as patterns, answers as data items matching the queries. Formally, an answer to a query is defined as a simulation  of an instance of the query in a data item.