These included misspellings, abbreviations and subsidiaries. Cleaning up legacy data, as well as recording changes, additions and deletions, becomes a major issue in making data warehouses work. To track these modifications, metadata information is created to describe the data that are loaded in the warehouse. Metadata tells users where the data came from, what reformatting or transformations were done to the data and when they were retrieved and loaded into the warehouse. Retrieving the data from existing systems is the first step in building a data warehouse.
Designers use connection or gateway tools to connect warehouses to existing legacy environments.
In many cases, data reside in IBM main frames. Commercial software exists to transfer and reformat these data, to create metadata information files and to formulate a data dictionary that describes everything in the warehouse. Data warehouse software packages are available from Visions Solutions, Carleton Corporation and Evolutionary Technologies. Data warehousing is a journey, not a destination, Workman emphasizes. He adds that the designer never finishes this is a process of refining, consolidating and building new ways to view and analyze data.