Why Separate Data Warehouse?
High performance for both systems
- DBMS— tuned for OLTP: access methods, indexing, concurrency control, recovery
- Warehouse—tuned for OLAP: complex OLAP queries, multidimensional view, consolidation.
Different functions and different data:
- missing data: Decision support requires historical data which operational DBs do not typically maintain
- data consolidation: DS requires consolidation (aggregation, summarization) of data from heterogeneous sources
- data quality: different sources typically use inconsistent data representations, codes and formats which have to be reconciled