When you select Database Schema as target for BIX extract, before extracting data to the target database you must first create a schema to match the extracted data. You can use BIX to generate an SQL file that creates the appropriate schema. For this ddl file name and path option. You can give the path which can be accessed by pega and when you run the extract rule you will get a button to generate DDL. When you click this button then the DDL will be generated in the path specified. You need to run this SQL in the DB to create appropriate table.