Difference bettween relational star shema and multidimensional modelin

[antonaras]

Hi everyone

I'm totally new in the field of data warehouse and i'm trying to write a project on data warehouse. The problem i can't understand the difference between relational modeling and multidimensional modeling.
All the reference i read talk about this subjects and the star schema. Can anyone anwer this simple question for me. is a star schema a relational Design approach or a multidimensional approach or something in the middle?

Thank you all in advance and i appologize for my stupid question

 

[Hans63]

Well, first of all: there are no stupid questions.

A star schema is different from a relation design, a.o. because it is not in third normal form. A star schema has redundant attributes. (e.g. in a customer dimension you would add an attribute with city-name instead of a key to a tabel with city-names).

A star schema is a way to model a multidimensional model. However, a star schema can be implemented in a relational Database (Oracle DB2, Sybase, MSSQL, etc.)

In fact a RDBMS can handle a query on a star-schema quite efficiently.

Hope this helps you along a bit. If you are entirely new to datawarehousing I recommend you to read some books and articles on this subject. The datawarehouse Toolkit by Ralph Kimball is a good book to start with. This handles star-schema's.

Bear in mind however that a datawarehouse does not nescecarily imply the use of a star-schema. Star schema's are a key feature of most datamarts, but a datawarehouse does not have to be modelled in a star schema.

 

[johnherman]

Hans63 has provided good info. Dimensional Modeling (i.e. star and snowflake schemas) is different from Relational Modeling. The typical dimensional model falls somewhere between First and Second normal form.

More important than the design at this point is to understand the basic reason for building a DW. I suggest you read faq353-6430. There are also a couple other useful faq's and there has been much good discussion in this thread, so a search could be helpful.


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