Qlik Catalog provides two mechanisms for process and defining XML sources. FirstGen XML is the default XML ingest. To configure NextGen XML refer to "Enabling NextGen XML" section in the Qlik Catalog install guide.
FirstGen XML ingest employs XSD language files to specify the structure and data types within XML for dataload environment preparation.
FirstGen XML: Extensible markup language overview
NextGen XML identifies and defines primary and foreign keys in the generated entity table from a source XML without the need for accompanying XSDs.