Before starting to subset a database, the subsetter will do a validation step to ensure that subsetting is likely to succeed. It will check the contents of the subsetting options JSON file make sense, and will compare its contents to the database being subsetted. If it finds any errors, subsetting will not start and the subsetter will exit with one or more validation errors.

Validation errors fall into two categories:

• file errors - there is an error in the subsetting options file
• database errors - there is an error in the database being subsetted (an incompatibility between the options file and the database, or a mismatch between the source and target databases)

Each validation error will have a help link associated with it. Following this link will explain more about the error, and show how to address it.