Dimensional modeling

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Dimensional modeling (DM) is the name of a logical design technique often used for data warehouses. It is considered to be different from entity-relationship modeling (ER). Dimensional Modeling, however, does not necessarily involve a relational database. The same modeling approach, at the logical level, can be used for any physical form, such as multidimensional database or even flat files. According to Dr. Kimball^[1], DM is a design technique for databases intended to support end-user queries in a data warehouse. It is oriented around understandability, contrary to database administration. According to him, although transaction-oriented ER is very useful for the transaction capture, it should be avoided for end-user delivery.

Dimensional modeling always uses the concepts of facts, AKA 'measures', and dimensions. Facts are typically (but not always) numeric values that can be aggregated, and dimensions are groups of hierarchies and descriptors that define the facts. For example, sales amount is a fact; timestamp, product, register#, store#, etc. are elements of dimensions. Dimensional models are built by subject area, e.g. store sales, inventory, claims, etc. Because the different subject areas share some but not all dimensions, efficiency in design, operation, and consistency, is achieved using conformed dimensions, i.e. using one copy of the shared dimension across subject areas. The term "conformed dimensions" was originated by Ralph Kimball.

[edit] References

• Ralph Kimball (1997). "A Dimensional Modeling Manifesto". DBMS and Internet Systems 10 (9). http://www.dbmsmag.com/9708d15.html.