XML and relational databases are the most commonly used data-sources for numerous Java-based enterprise applications. The ever-growing dependence of Java-based applications on these technologies calls for developing a uniform means of querying these data-sources in the Java layer such that queries written for any of these technologies look similar and are in fact governed by a single grammar. This thesis implements a new backend system encapsulating querying capabilities over XML and JDBC based relational databases which would complement the translation of queries written using QuEL [1], a language extension to the Java programming language. The QuEL language extension to Java is part of another thesis developed previously and acts as the query language for the back-end implemented in this thesis for XML and relational databases. The benefits of this approach include faster development time and a flat learning curve towards a single query language for various data sources
