LDR bytes 20-23 show as already corrected in before record when Preview in GDC

Question

Many bib records are lacking the required '4500' value in MARC Leader bytes 20-23. I would like to fix these with Global Data Change (GDC), but when I view a record with bad values in GDC preview, it shows me the correct leader value in the before record. And if I use "does not equal" 4500 as the Condition in the Data Change Rule Set, the record is not changed. What's going on?

Answer

GDC is coded to automatically change LDR 20-23 to 4500 before parsing out the rules for the job. Because of this, the records all have LDR 20-23 equal 4500 before GDC gets to processing the rule. If we look at the order things are happening in, it's something like 

1. Data Change Job submitted 
2. Data Change Job started 
3. GDC changes LDR 20-23 to 4500 
4. GDC looks at rules to see what condition must be met. 
5. Record already contains LDR 20-23 = 4500 because #3 
6. GDC determines condition is not met 
7. Records written to unchanged file and not updated. 

As long as the records have been identified, using a rule condition that can definitely be met - something like MARC Control Field Exists (LDR) should work to successfully update LDR 20-23.

• Article last edited: 27-Oct-2016