HEADER segment format

The IMS catalog HEADER segment type, also called the resource header, is the root segment type for the IMS catalog database.

The resource header for an IMS catalog database record contains information about the type of metadata that is stored in that record. The resource header indicates whether a specific IMS catalog record contains DBD or PSB metadata and includes the IMS name and alias name of the resource that the catalog record describes.

The root key for a catalog record is the value of the RHDRSEQ field in this segment. This key value is generated by the IMS catalog populate utility (DFS3PU00) or the ACB generation and catalog populate utility (DFS3UACB). The value is created by concatenating the record type and the IMS member name of the resource. The record type is eight characters long and is right-padded with blank characters. The IMS member name is always eight characters long.

For example, this is the root key for a DBD record with the name ACF12000:

DBD     ACF12000

This is the root key for a PSB record with the name MXG88888:

PSB     MXG88888

The root key value is also used to sort catalog records into database partitions if your catalog database consists of more than one partition. The partition high key for the last partition in the database must be high enough to contain the highest-key record in the catalog.

Segment name
HEADER
Parent name
Not applicable
Sequence field
RHDRSEQ
Segment length
56 bytes
Table 1. HEADER segment map
Offset (bytes) Length (bytes) Data type Field name Description Unique key field
1 2 X LEN Length of this resource header segment  
3 2 X CTL Control field  
5 2 X SEQNUM Segment sequence number  
9 16 C RHDRSEQ Sequence field, type = U X
  9 8 C TYPE Type of resource metadata in this catalog record  
17 8 C IMSNAME Name of the resource described in this catalog record  
25 4 X RETNINST The minimum number of instances of the DBD or PSB that must be kept in this record when record segments are deleted. This value is modified with the UPDATE statement of the IMS Catalog Record Purge utility. If you do not provide a value for this field, the utility uses the value specified on the RETENTION statement in the CATALOG section of the DFSDFxxx member of the IMS.PROCLIB data set.  
29 4 X RETNDAYS Minimum number of days to keep each instance of the DBD or PSB in this record before the instances is eligible for deletion. This value is modified with the UPDATE statement of the IMS Catalog Record Purge utility. If you do not provide a value for this field, there are two possible scenarios:
  • If the RETNINST field contains a value of 1 or greater, the IMS Catalog Record Purge utility does not purge instances of this DBD or PSB based on their age.
  • If the RETINST field contains 0, the IMS Catalog Record Purge utility uses the values specified in the DFSDFxxx member to determine the retention criteria for the DBD or PSB instances in this record.
  
33 8 C FILLER1 Reserved  
41 7 C ACTTS Active record timestamp in packed format. Identifies the timestamp of the active member.  
48 7 C PNDTS Pending record timestamp in packed format. Identifies the timestamp of the pending member.  
55 2 C FILLER2 Reserved  
57 13 C PACTTS Active record timestamp in expanded printable format. Identifies the timestamp of the active member.  
70 13 C PPNDTS Pending record timestamp in expanded printable format. Identifies the timestamp of the pending member.