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Note: In the context of performance tuning, it is intentional and acceptable to duplicate data in entities. When data is normalized across multiple entities instantiated as multiple tables that must be joined together, the Oracle server processes need to physically fetch data from multiple tables and join them in memory buffers to produce the required results set. The extra IO required to query or manipulate normalized data sometimes justifies denormalizing data models to reduce disk IO operations and hence increase performance. This is common in Data Warehouse (DWH) and Decision Support Systems (DSS) but is an exception rather than the rule in Online Transaction Processing (OLTP) systems.