A description of the three stages follows. The user must explicitly identify the data services to the used. The data control facility provides the necessary control commands, data transformations, and accessing methods. A single request would include the use of several interacting services. The data control facility is not necessarily located at his local Host.
All references are by name.
For example, data could be retrieved from several files, each managed by a different data management system. The data control facility must be cognizant of the location of data files, their structure, data management system capabilities, etc. In any case, a common means is desirable for handling applications such as file transfer, on-line update and retrieval of data, information gathering and reporting, and program access to data. The language should be designed to facilitate the resolution of physical discrepancies in data and file structures. The user should be able to superimpose logical restructuring of data without any change in the physical structure.