IMS DB DL/I Terminology - IMS/DB

What is IMS DB DL/I Terminology?

Hierarchical databases work at the relationships between two or greater segments. The subsequent instance suggests how segments are associated with every other in the IMS database structure.

ims_database

Root Segment

Points to note:

  • The segment that lies at the top of the hierarchy is called the root segment.
  • The root segment is the only segment through which all dependent segments are accessed.
  • The root segment is the only segment in the database which is never a child segment.
  • There can be only one root segment in the IMS database structure.
  • For example, 'A' is the root segment in the above example.

Parent Segment

Points to note:

  • A parent segment has one or more dependent segments directly below it.
  • For example, 'A', 'B', and 'E' are the parent segments in the above example.

Dependent Segment

Points to note:

  • All segments other than the root segment are known as dependent segments.
  • Dependent segments depend on one or more segments to present complete meaning.
  • For example, 'B', 'C1', 'C2', 'D', 'E', 'F1' and 'F2' are dependent segments in our example.

Child Segment

Points to note:

  • Any segment having a segment directly above it in the hierarchy is known as a child segment.
  • Each dependent segment in the structure is a child segment.
  • For example, 'B', 'C1', 'C2', 'D', 'E', 'F1' and 'F2' are child segments.

Twin Segments

Points to note:

  • Two or more segment occurrences of a particular segment type under a single parent segment are called twin segments.
  • For example, 'C1' and 'C2' are twin segments, so do 'F1' and 'F2' are.

Sibling Segment

Points to note:

  • Sibling segments are the segments of different types and the same parent.
  • For example, 'B' and 'E' are sibling segments. Similarly, 'C1', 'C2', and 'D' are sibling segments.

Database Record

Points to note:

  • Each occurrence of the root segment, plus all the subordinate segment occurrences make one database record.
  • Every database record has only one root segment but it may have any number of segment occurrences.
  • In standard file processing, a record is a unit of data that an application program uses for certain operations. In DL/I, that unit of data is known as a segment. A single database record has many segment occurrences.

Database Path

Points to note:

  • A path is the series of segments that starts from the root segment of a database record to any specific segment occurrence.
  • A path in the hierarchy structure need not be complete to the lowest level. It depends on how much information we require about an entity.
  • A path must be continuous and we cannot skip intermediate levels in the structure.
  • In the following figure, the child records in dark grey color show a path which starts from 'A' and goes through 'C2'.

child_record

All rights reserved © 2018 Wisdom IT Services India Pvt. Ltd DMCA.com Protection Status

IMS/DB Topics