Chained Set Management › Chained Sets › Disconnecting Records

Disconnecting Records

Operations Performed

To disconnect a record occurrence from a chained set without erasing the record occurrence, CA IDMS/DB must update pointers in the current, prior, and next records, as described next:

• For the record being disconnected, CA IDMS/DB adjusts all the record occurrence's pointers to null (minus 1) for the set from which the record is being disconnected.
• For the prior record in the chain, CA IDMS/DB adjusts the next pointer for the set from which the record occurrence is being disconnected so that the prior record points to the next record.
• For the next record in the chain (if the set has prior pointers), CA IDMS/DB adjusts the prior pointer for the set from which the record occurrence is being disconnected so that the next record points to the prior record.

The following diagram shows disconnecting a record. The EMPLOYEE 19 record is disconnected from the DEPT-EMPLOYEE set for DEPT 3100. EMPLOYEE 19's pointers for that set are changed to null. The prior pointer in the EMPLOYEE 23 record is adjusted to point to the DEPT 3100 record, while the next pointer in the DEPT 3100 record must be adjusted to point to the EMPLOYEE 23 record.

Adjusting the Pointer

To adjust the next pointer in the prior record, CA IDMS/DB must access the prior record. In a set without prior pointers, however, CA IDMS/DB must walk the entire set to access the prior record. For this reason, prior pointers are typically included in all sets to which the DISCONNECT (or ERASE) DML command might be applied.