I have several queries here
1.Datawarehouse contains historical data.If any updations occur in data,how can we update these changes to existed data in datawarehouse.Do we need to write any code.Is the process of applying changes will different to database(oracle..etc) to database(teradata etc).
2.genrally Datawarehouse divides into datamarts.How this will be happen.Is datamart exists in Datawarehouse or will it exists in some other database.Do we need to apply any other process (eg:ETL) to create Datamarts.
3.I have read a statement "While we are loading data into datawarehouse we select data which is relevent and useful to business users".How can we identify this ,Why dont we select whole data.may it contains duplicates.Except this what are the other reasons.
4.What are the differences between ETL and ELT.Which is better one.
Thanks & Regards