On wrapping query languages and efficient XML integration

Modern applications (Web portals, digital libraries, etc.) require integrat ed access to various information sources (from traditional DBMS to semistru ctured Web repositories), fast deployment and low maintenance cost in a rap idly evolving environment. Because of its flexibility, there is an increasi ng interest in using XML as a middleware model for such applications. XML e nables fast wrapping and declarative integration. However, query processing in XML-based integration systems is still penalized by the lack of an alge bra. with adequate optimization properties and the difficulty to understand source query capabilities. In this paper, we propose an algebraic approach to support efficient XML query evaluation. We define a general purpose alg ebra suitable for semistructured or XML query languages. We show how this a lgebra can be used, with appropriate type information, to also wrap more st ructured query languages such as OQL or SQL. Finally, we develop new optimi zation techniques for XML-based integration systems.