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Reorganization for logically related databases

Logical relationships provide a user-defined access path to data.

Logical relationships are typically established by a special set of pointers: logical parent (LP) and logical child (LC).

Logical pointers can be symbolic or direct. A symbolic pointer uses the logical parent concatenated key (LPCK) to point to the logical parent segment. A direct pointer uses the RBA to point to the logical parent or logical child segment.

When a database is reorganized, all segments in the database are often moved to different locations. Consequently, all direct pointer references to the segments must be updated during the reorganization. Symbolic pointer references do not require an update because they use the LPCK.

The logical relationship is either internal or external.

  • Internal—LP and LC are in the same database.
  • External—LP and LC are in different databases.
Warning

Note

For a comprehensive explanation of logical relationships, refer to the IBM IMS/ESA Administration Guide: Database Manager.

Related topic

JCL Requirements—Reorg function (Fast Reorg Facility/EP)

The following figure depicts three types of logical relationships.

  • Internal logical relationship
  • External logical relationship with symbolic pointers only
  • External logical relationship with direct pointers

The internal logical relationship is between two segments in the same database D1. The logical child segment D1S3 points to the logical parent segment D1S2 using the LPCK of the logical parent. The LPCK of the logical parent is stored in the data portion of the logical child. The logical parent does not point back to the logical child.

The external logical relationship with symbolic pointers only is between a logical child segment D1S5 in D1 and a logical parent segment D2S1 in D2. The nature of the relationship is the same as the internal logical relationship only the segments reside in different databases.

The external logical relationship with direct pointers is a bidirectional relationship between a logical child segment D1S4 in D1 and a logical parent segment D2S3 in D2. The logical child points to the logical parent using the LPCK of the logical parent. The logical parent points back to the logical child using the RBA of the logical child. The RBA of the logical child D1S4 is stored in the prefix of D2S3.

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BMC AMI Online Reorg for IMS 5.2