data validation Datawarehouse ETL
Usually surrogate keys are implemented based on dimension tables and external data sources in order to have coherent and valid data records; the ETL process, which in charge of extracting data from different sources, transforming and finally delivering data into the data warehouse, must ensure this condition (i.e., surrogate keys refer to the right record). 
Personally, I did perform a data validation once by simply using a comparison between the OLAP(i.e., Data Warehouse) result and OLTP(i.e., DB sources) result for the same simple analysis query in order to see if there are any incoherent information.