Relationship between segments

One final term for describing segments is twin segment. Twin (like root, dependent, parent, and child) describes a relationship between segments. Twin segments are multiple occurrences of the same segment type under a single parent.

In the following figure, the segments Baker and Coe are twins. They have the same parent (Math), and are of the same segment type (STUDENT). Pass and Inc are not twins. Although Pass and Inc are the same segment type (GRADE), they do not have the same parent. Pass is the child segment of Baker, and Inc is the child segment of Coe.

Figure 1. Segment occurrences in a school database record

The following topic discusses the hierarchy in more detail. Subsequent topics describe the objects in a database, what they consist of and the rules governing their existence and use. These objects are:

• The database record
• The segments in a database record
• The fields within a segment