W.H Inmon’s Approach
According to Bill Inmon who is considered as the father of Data Warehouse, “A Data Warehouse is a subject oriented, integrated, nonvolatile, and time variant collection of data in support of management’s decisions.” Contrary to an operational system where data is stored by operational applications, in data warehouse, data is stored by business subjects. The data in a data warehouse usually comes from diverse data sources. Using ETL process the inconsistencies in the source data is removed and data elements are standardized before storing the data into a data warehouse. The data in a data warehouse is time variant in nature as it contains historical data. Inmon proposes a top-down ( create first model approach to create a centralized Enterprise Data Warehouse using traditional database modeling techniques (ER Model), where the data is stored in 3NF. For the development of this large data warehouse, Inmon suggests a spiral development iterative method, where small parts of relational database are added to the data warehouse on iteration. This approach permits granularity of data and provides maximum flexibility to create new optimized dimensional data marts according to the current requirements of an enterprise. The data warehouse acts as data source for the new datamarts .
Example: “Top Down” Development