Why Separate Data Warehouse?

Performance

·        Operational database designed & tuned for known transaction workloads.

·        Complex OLAP queries would degrade performance of transaction.

·        Special data organization, access & implementation methods needed for multidimensional views & queries.

Function

·        Missing data:  Decision support requires historical data, which Operational database do not typically maintain.

·        Data consolidation: Decision support requires consolidation (aggregation, summarization) of data from many heterogeneous sources:  Operational database, external sources.

·        Data quality:  Different sources typically use inconsistent data representations, codes, and formats which have to be reconciled.