DL/I and CA IDMS/DB › DL/I and CA IDMS/DB Correspondences › Sequenced and Unsequenced Child Segments

Sequenced and Unsequenced Child Segments

CA IDMS/DB requires different definitions for child segments, depending on whether they are sequenced or unsequenced.

Sequenced Child Segments

Sequenced child segments correspond to member record types in sorted sets. The child segment's sequence field is used for the sort key in the CA IDMS/DB sorted set.

• If the child segment is defined for U (unique) sequence field values, duplicates are not allowed for the set (DUPLICATES NOT ALLOWED).
• If the child segment is defined for M (multiple or duplicate) sequence field values, the value for the insert RULES parameter determines where duplicate fields are stored within the set sequence:
  • FIRST ── the set is ordered DUPLICATES FIRST.
  • LAST ── the set is ordered DUPLICATES LAST.
  • HERE ── the corresponding record type is a member in an unsorted set with a set order option of PRIOR.

Unsequenced Child Segments

Unsequenced child segments correspond to member record types in unsorted sets. The set ORDER option is determined by the value for the RULES parameter on the child's SEGM statement:

• HERE ── Corresponds to an order option of PRIOR.
• FIRST ── Corresponds to an order option of FIRST.
• LAST ── Corresponds to an order option of LAST. Note that LAST is the DL/I default for unsequenced segments. If a child segment does not have RULES specified, LAST is used for the order option in the corresponding unsorted set.