http://www.vgrdl.de or https://www.destatis.de/EN/Service/FAQ/NationalAccounts/Revision2014/Changes.html
The biggest change in the data of Revision 2011 ist that of the classification of economic activity (=Wirtschaftszweig =WZ). With each review of the classification former groups can't be compared to current groupings, therefore older data is not comparable to the new data.
The most current classification system is WZ08, and replaces WZ03, data according to WZ08 is currently only available from 2008, and data according to WZ03 ends in 2009.
For further Details please go to: http://www.destatis.de/themen/e/thm_volksw.htm
Calculations and definitions follow the European System of Accounts, ESA 1995 Revision 2005.