A data warehouse is a subject-oriented, integrated, time-variant and non-volatile collection of data in support of management’s decision making process.
1.Top-Down Approach OR Bill Inmon Approach:
2.Bottom-UP Approach OR Ralph Kimball Approach:
Ralph Kimball and Bill Inmon are innovators of data warehousing space and they have offered unique approach towards enterprise data warehousing. There is no right or wrong approach and it totally depends on kind of requirement, project nature to decide the approach to follow.
|Process||Ralph Kimball||Bill Inmon|
|Approach||1. It is known as Bottom-UP Approach.||1. It is as Top Down Approach.|
|Maintenance||2. Easy to maintain.||2. Difficult, often redundant and to revisions.|
|Time||3. Longer start-up time.||3. Short time for initial set-up.|
|Building of Data warehouse||4. Takes more Time||4. Takes lesser time|
|Cost||5.High Cost initially, but Subsequent project development cost will come down.||5.Low Cost initially, but each Subsequent stage will cost nearly the same.|
|Skill set||6.Specialist team||6. Generalist team|
The data mart is a subset of the data warehouse that is usually oriented to a specific business area or Department. Data marts are small slices of the data warehouse. Whereas data warehouses have an enterprise-wide depth, the information in data marts pertains to a single department.
|Data Warehouse||Data Mart|
|Data Warehouse holds all subject areas in organization.||Data Mart holds only one subject area. Ex Sales or Finance in organization.|
|All data sources are integrated||Given subject are sources are integrated|
|Detailed information||Holds more summarized data. (Many holds full detail)|
|Does not necessarily use a dimensional model but feeds dimensional models.||Is built focused on a dimensional model using a star schema.|