Basic Segment Types

The following list contains a detailed description of the various segment types and their interrelations within a hierarchical data structure. Refer to Figure 7-3 on page 71 and Figure 7-4 while reading these descriptions.

Figure 7-4. Segment Types and Their Relationships

• The segment on top of the structure is the root segment. Each root segment normally has a key field that serves as the unique identifier of that root segment, and as such, of that particular database record (for example, the part number). There is only one root segment per database record.

• A dependent segment relies on the segments above it in the hierarchy for its full meaning and identification.

• A parent/child relationship exists between a segment and its immediate dependents.

• Different occurrences of a particular segment type under the same parent segment are called twin segments.

• Segment occurrences of different types under the same parent are called sibling segments.

• A single segment can be a dependent and a child simultaneously. For example, in Figure 7-4, segment DETAIL 211 is a dependent of segment ORDER 21 and of root segment PART 2 and also a child of segment ORDER 21.