Data summarization and even denormalization has a much lower penalty since update performance is much less visible. Table 3 illustrates how the requirements and success factors are different for an operational system compared to a data warehouse. The warehouse is used by knowledge workers or management who want to analyze data to help improve the running and management of business over the longer term. Requirements Requirements are generally defined ahead of time to support well defined business operations. Requirements are often unknown to begin with.
Requirements emerge as the data warehouse is used to support decision making.
The application must provide efficient performance which includes fast real time updates, high availability and data integrity. The application must provide access to a wide array of standardized and well integrated data. The architecture must be flexible so that data can be adjusted and new tools used. Few organizations undertake the building of a data warehouse all at once. The effort of building a complete, consolidated data warehouse would require an enormous effort and would take too long.