A data warehouse stores historical data that is collected from various sources and the data is time variant. The data warehouse is updated in a scheduled and controlled manner. An online system usually does not store historical data, however if history data is stored it would pose severe performance issues, further being an Online environment 2 users accessing the same set of information are likely to derive different results. An online system would provide data only from a single source, whereas a data warehouse usually has data being put in from various sources.
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