Embedded in UnityJDBC is a relational database engine and associated operators of selection, projection, grouping, ordering, and join. You can build your own global query spanning data sources by combining these operators into an execution tree. In the distribution is a file called ExampleEngine.java which demonstrates how to use the engine to build an execution tree. Also in this file is an example on how you can have Unity parse but not execute a global query. UnityJDBC will return its global query and execution plan which you can later execute. This feature gives you the opportunity to modify the global execution plan before execution if desired. It also allows you to track the progress of a global query at the operator level.