Top-Down vs Bottom-Up Approach

Inmon’s top-down approach

Inmon defines data warehouse as a centralized repository for the entire enterprise. Data warehouse stores the ‘atomic’ data at the lowest level of detail. Dimensional data marts are created only after the complete data warehouse has been created. Thus, data warehouse is at the center of the Corporate Information Factory (CIF), which provides a logical framework for delivering business intelligence.

Inmon defines the data warehouse in the following terms:

1. Subject-oriented: The data in the data warehouse is organized so that all the data elements relating to the same real-world event or object are linked together
2. Time-variant: The changes to the data in the database are tracked and recorded so that reports can be produced showing changes over time
3. Non-volatile: Data in the data warehouse is never over-written or deleted -- once committed, the data is static, read-only, and retained for future reporting
4. Integrated: The database contains data from most or all of an organization's operational applications, and that this data is made consistent

Kimball’s bottom-up approach

Keeping in mind the most important business aspects or departments, data marts are created first. These provide a thin view into the organizational data, and as and when required these can be combined into a larger data warehouse. Kimball defines data warehouse as “A copy of transaction data specifically structured for query and analysis”.

Kimball’s data warehousing architecture is also known as Data Warehouse Bus (BUS). Dimensional modeling focuses on ease of end user accessibility and provides a high level of performance to the data warehouse.

Inmon vs. Kimball: Similar or different?

"You can catch all the minnows in the ocean and stack them together and they still do not make a whale." ~Inmon “The data warehouse is nothing more than the union of all the data marts" ~Kimball

Pros and cons of both the approaches

Courtesy:Sansu George is a business analyst at ABIBA Systems

http://searchbusinessintelligence.techtarget.in/tip/Inmon-vs-Kimball-Which-approach-is-suitable-for-your-data-warehouse