Root segment

Only one root segment exists within a database record. All other segments in the database record are called dependent segments.

In the example shown in How data is stored in a database, the COURSE segment is the root segment. The segments INSTR, REPORT, STUDENT, GRADE, and PLACE are the dependent segments. The existence of dependent segments hinges on the existence of a root segment. For example, without the root segment COURSE, there would be no reason for having a PLACE segment stating in which room the course was held.

The third level of dependent segments, REPORT and GRADE, is subject to the existence of second level segments INSTR and STUDENT. For example, without the second level segment STUDENT, there would be no reason for having a GRADE segment indicating the grade the student received in the course.