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What are the differences between ODS, EDW and a central repository and their specific uses?

Question: What are the differences between ODS, EDW and a central repository and their specific uses? We have delivered several subject-specific data marts to the business. The task at hand is to reverse engineer the denormalized star schema data mart data into a more normalized structure.  The reason behind this project is to have the capability to provide other data marts that will help to answer business questions which cannot be answered with the existing marts.  I struggle with whether we need to build an ODS, EDW or a central repository/CIF.

 

Chuck Kelley’s Answers:  If you already have data marts, then you are going to reverse engineer to the enterprise data warehouse (EDW) (or Central Repository).  The ODS (Operational Data Store) is a production database used to bring multiple sources together into a single normalized, partially integrated database to do operational reports.  Then the ODS and the balance of the operational systems should comprise the EDW (Enterprise Data Warehouse).  From there, you build your data marts.

 

I am not sure that it is necessary to denormalize the star schema data mart data in order to accomplish this.

Larissa Moss' Answer: An ODS is a database that is subject-oriented, integrated, volatile and current. It is usually used by business managers, analysts or customer service representatives to monitor, manage and improve daily business processes and customer service. An ODS is often loaded daily or multiple times a day with data that represents the current state of operational systems. An EDW is a database that is subject-oriented, integrated, non-volatile (read-only) and time-variant (historical). It is usually used by financial analysts for historical trend analysis reporting, data mining and other activities that need historical data. An EDW keeps growing as you add more historical snapshots, either daily, weekly or monthly. Because an EDW has historical data (and the ODS usually does not), some companies use the EDW as a hub for loading their data marts. CIF stands for Corporate Information Factory in the context of data warehousing. CIF is an overall architecture that includes ODS, EDW, data marts, oper marts, exploration warehouse, meta data repository, extract, transfer and load (ETL) processes, portals, OLAP and BI applications like dashboards and scorecards, and so on. Since the question was about data mart consolidation, the other option you have is to create a normalized persistent staging area (PSA) database, which is not accessible by end users but serves as a hub for loading your current and future data marts.


Chuck Kelley is an internationally known expert in database and data warehousing technology. He has 30 years of experience in designing and implementing operational/production systems and data warehouses. Kelley has worked in some facet of the design and implementation phase of more than 50 data warehouses and data marts. He also teaches seminars, co-authored four books on data warehousing and has been published in many trade magazines on database technology, data warehousing and enterprise data strategies. He can be contacted at chuckkelley@usa.net.

Larissa Moss is founder and president of Method Focus Inc., a company specializing in improving the quality of business information systems. She has more than 20 years of IT experience with information asset management. Moss is coauthor of three books: Data Warehouse Project Management (Addison-Wesley, 2000), Impossible Data Warehouse Situations (Addison-Wesley, 2002) and Business Intelligence Roadmap: The Complete Project Lifecycle for Decision- Support Applications (Addison-Wesley, 2003). Moss can be reached at methodfocus@earthlink.net.

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