Pattern Queries for XML and Semistructured Data

Abstract

Query and transformation languages developed since the mid 90es for XML and semistructured data e.g. XQuery, the precursors of XQuery, and XSLT built 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 from regular expressions such as *, +, '?, and "wildcards" give rise to a flexible node retrieval from incompletely specified data items. This paper investigates an alternative approach to querying XML and semistructured data. 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 [1] of an instance of the query in a data item. The basic