When deleting entries in the DescRec table, a number of triggers may need to be handled. Logical links to other DescRec entries is one of them. As described in the LabelRec section of this appendix, use fetch and update to modify the logical link to another parameters or set the values to NULL.

Another common trigger is with the CrtFixed table. In general, entries in the CrtFixed table pointing to the DescRec entry you wish to delete are no longer needed. Use a SQL delete command to delete these records.

CrtDCpnt and CrtICpnt table triggers are more involved. These two tables can have entries that point to more than just a single DescRec entry. Because of this, care must be taken to remedy the trigger. First, use the fetch to identify the entry that reference the DescRec entry. Look at each entry and determine if any other DescRec entries will be affected by the deletion of the entry in the Crt table. If no other DescRec entries will be affected, it is safe to delete the record. If other DescRec entries are affected, the typical action is to set the Label/RefName in the offending Crt table entry to NULL.

Triggers may also be caused by the NumList or NumPoint tables. If a trigger is with the NumList table, it is most likely the case that one wants to delete the numeric chain. To do this, find the NumList entry corresponding to the DescRec you wish to delete. Use the RecId from the NumList table to remove based on the MrecId in the NumPoint table. Then remove the NumList entry using the same RecId.

  sample1=> DELETE FROM NumPoint WHERE MrecId=112;
  DELETE 3

  sample1=> DELETE FROM NumList WHERE RecId=112;
  DELETE 1

If the offending record is simply a NumPoint entry, more steps must be taken. Since the NumPoint table relies on sequential RecId numbers to function properly, removing a RecId in the middle of a chain causes a need to shuffle the RecId numbers up. For example, the Label/RefName we want to delete from DescRec is RecId 3 in a list of five NumPoint actions. If the NumPoint record is deleted from the table, a sequence of 1,2,4,5 is left. This is not acceptable. To correct this, change the RecId of the fourth entry to 3, and the fifth entry to 4. After a fetch to verify your changes, you will notice that you now have 1,2,3,4,5 again, with 4 and 5 being identical. Delete the fifth record. Attempt the delete on the DescRec entry again.

Much like the triggers from the numeric chains, the triggers for the interlock chains can require extra steps. The same principles apply to deleting an entire chain. Perform a delete based on the RecId from ChkList, using MrecId in ChkPoint, ChkAct, and ChkAlarm. Then perform the delete based on the RecId in ChkList itself.

If the offending record is an entry in ChkPoint, remove and shuffle the RecId as was described for the NumPoint table. After shuffling the RecIds, correct the Offset values for the entries to remove the dead space left by the deleted entry. For example, the previous chain had 5 checks, each of them containing a single bit of offset. The third check was deleted. The offsets of the old RecId 4 and 5 (new RecId 3 and 4) should be changed to 2 and 3 repectively. In addition, the Mask and Mask2 fields in the ChkAct and ChkAlarm tables must be updated to reflect the deletion of the ChkPoint entry.