ApproXQL: Design and Implementation of an Approximate Pattern Matching Language for XML

We introduce the simple query language approXQL, which supports hierarchical, Booleanconnected query patterns. The interpretation of approXQL queries is founded on cost-based query transformations: The total cost of a sequence of transformations measures the similarity between a query and the data and is used to rank the results. We describe in detail the implementation of the approXQL query processor, which uses an expanded query representation and sophisticated indexes to compute all results of a query in polynomial – typically sublinear – time with respect to the database size.