The Central Credit Committee (German Zentraler Kreditausschuss / ZKA) is an industry association of the German banking industry. It was renamed to Die Deutsche Kreditwirtschaft (DK) in August 2011
The user guides can be found from ebics: http://www.ebics.de
Validator uses guide: Annex_3_DataFormatsV2.6.pdf
DK uses a stripped version of ISO 20022 schema. This means myriad of institution specific rules are already limited from schema level, and using elements which would be ignored in EPC pipes will cause a failure from schema level in DK pipes.