Data Warehousing - what is dimension modeling?

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what is dimension modeling?

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Last Update: July 09, 2007 Asked by: ravindra kumar

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July 31, 2006 07:44:08

anwar_pat

Member Since: March 2006 Contribution: 1

RE: what is dimension modeling?

It is a logical design technique that seeks to present the data in a standard, intuitive framework that allows for high-performance access.There are different data modelling concepts like ER Modelling(ENtity Relationship modelling) ,DM (Dimensional modelling),Hierarichal Modelling,Network modelling.But popular are ER and DM only.

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July 09, 2007 10:22:45

Hakoonamatata

Member Since: July 2007 Contribution: 5

RE: what is dimension modeling?

Here's a different way to look at dimensional modelling:

Consider data to be a flat table for now. It would have some columns that contain numbers that need to be used in calcualtions later (e.g. basic salary). It would also have some columns that conatin non-numeric data, that serve as the basis of grouping data and filtering (e.g. Job position, location etc.). The 3rd aspect is the possible statistical functions that one can subjet the numeric data to (e.g. Average, Min, Max, Percentiles etc.).

All reports are a combination of the above 3 aspects.

All the columns that can be used for grouping / filtering data are called dimensions (at a higher level) while all numeric columns are calles Facts or measures.

A data model that maintains all the dimensions in their own tables and the fact in a separate table (with the necessary relationships with all dimensions), is called Dimensional Model. This is a de-normalised model as this is used for report generation. The only data feeds can be through a scheduled and structured process (ETL) which in turn fetches data from a relational / transational data source(s).

For deeper knowledge, look for the same in Ralph Kimball guide to Dimensional Modelling.

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