IMS, VSAM and Flat files are the most common source of invalid data conditions because validation of data type, format and content is the responsibility of the source application programmer. While the best solution might be to correct the application responsible for creating the invalid data and correcting the existing invalid data in the source database, the most common solution is to simply prevent the invalid data from being propagated. The INVALID Command, changes the value of any field determined to be invalid by to one of four values or to explicitly trigger an exception which will cause the Apply Engine to terminate:
- Null
- Spaces
- Zero
- "constant" value
- Exception
It is up to the script developer to specify the INVALID command. The INVALID command is typically added to scripts as they are tested and invalid data is identified. It is important to use data as much like production data as possible in the later stages of testing to ensure that this condition is identified prior to production implementation, the alternative is that the Engine will terminate in production at the first record containing invalid data.