The exit point lists the entry that matches a certain label and type. You can use the exit to check fields in a record and decide whether to use the record. The exit sets a return code that specifies whether to use the record or not. Use the exit_data parameter in the service to specify what the exit should use as a search value.
For example, you can use the CKDS entry retrieval exit to perform a specific search of the installation data field. An installation can specify whatever it chooses to in the installation data field. The exit can select a record that matches a certain key label and key type. You can check the record and accept or reject it based on the installation data field.