A method of retrieving data from any one of a plurality of data sources is disclosed. The data stored by each data source are arranged according to an associated data format. The method comprises: issuing a retrieval request for data stored on a designated one of the plurality of data sources to a control process; passing the retrieval request from the control process to the one a plurality of retrieval processes that is associated with the designated data source, said one of the retrieval processes retrieving the requested data from the designated data source and rearranging the retrieved data into a common output format, if it is not already in the common output format; and passing the data in the common output format to the control process.