While loading worker data through HDL, we can ensure that the person duplicate check is done,i.e. the same person does not exist in the system already, by using the PersonDuplicateCheck attribute of the Worker object.
If at the enterprise level we have a duplicate check enabled that will anyways be checked while loading the data for all the records, but if the duplicate person check is set to None at enterprise level, using this attribute we can do the duplicate person check at the record level in HDL/HSDL.
Another important point to remember is to ensure that the formatting of the field being validated for duplication should be maintained, otherwise the validation may fail.
Please see the below note from Doc ID 2340648.1
NOTE: The enterprise option Person Creation Service Duplicate Check controls whether checks for duplicate person records occur by default when you load person records in bulk. If you exclude the PersonDuplicateCheck attribute of the Worker object, then the current setting of Person Creation Service Duplicate Check applies. If you include the PersonDuplicateCheck attribute, then the current setting of Person Creation Service Duplicate Check is ignored for the relevant person record.
Customer must include any formatting characters in the value that you specify on the NationalIdentifierNumber attribute of the Person National Identifier component. For example, to load the US social security number 123-45-6789, you must include the hyphens.
Don't specify the number as 123456789. If you omit the formatting, then duplicate record checks are likely to fail.