1. A computing system comprising: an enterprise software application configured for issuing a query in accordance with a query language; a data source; and a data access service configured for executing on a computing environment between the enterprise software application and the data source, wherein the data access service includes: one or more decoration rules; a query planner, configured for receiving the query and a report specification from the enterprise software application, and for creating a run tree to facilitate retrieving query results from the data source, wherein the run tree comprises a sequence of executable decoration nodes; a query execution engine, configured for receiving the query from the query planner and executing the query on the data source, thereby providing a query result set comprising query results drawn from the data source that are responsive to the query; and wherein the run tree is configured for executing the sequence of decoration nodes on the query result set, wherein each of the decoration nodes modifies the query result set, thereby producing a decorated result set based on the query result set and the one or more decoration nodes, wherein each of one or more of the decoration nodes modifies the query result set in accordance with a corresponding one of the decoration rules, wherein producing the decorated result set comprises associating one or more members or values in the query results with a corresponding position or a calculated member in the report specification.