The Query Language TQL

This work presents the query language TQL, a query lan- guage for semistructured data, that can be used to query XML files. TQL substitutes the standard path-based pattern-matching mechanism with a logic-based mecha- nism, where the programmer specifies the properties of the pieces of data she is trying to extract. As a result, TQL queries are more 'declarative', or less 'operational', than queries in comparable languages. This feature makes some queries easier to express, and should allow the adoption of better optimization techniques. Through a set of exam- ples, we show that the range of queries that can be declar- atively expressed in TQL is quite wide. The implementa- tion of TQL binding mechanism requires the adoption of non-standard techniques, and some of its aspects are still open. In this paper we implicitly report about the current status of the implementation by writing all queries using the version of TQL that has been implemented, and that can be freely downloaded from //tql.di.unipi.it/tql.