Question

Data Warehouse Design, Fact table with 40 attributes

Asked by: andy_routledge

I am designing a data warehouse for a telecoms company. I have read several books and articles on data warehousing including Kimballs book on Dimensional Modelling and come up with a draft design for one of the core processes.

My design has 13 Dimensions which according to kimball is perfectly legal (5 to 15 is ideal) however my fact table has a total of 40 attributes approximately half of these are facts and the others are foreign keys. Now Im using roles in my fact table where attributes are the same. For example i have 2 dimensions date and time. Each record in the fact table has 6 aliases of this

call_start_date_key
call start_time_key
call_answer_date_key
call_answer_time_key
call_end_date_key
call_end_time_key

So although theses 6 FK's theres actually only 2 dimensions. In my design i have at least 3 occasions where this sort of thing happens. My question is have I created a design that centipedes or is this perfectly fine? I'm slightly worried that although all 40 attributes in the fact table are integer or number type there are way too many. Theres no way i can drop any of them either as there things such as call duration weekend and call total retail duration. Any input on this would be greatly appreciated

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Asked On
2007-07-10 at 03:58:25ID22685550
Tags

fact

,

table

,

data

,

warehouse

,

design

Topics

OLAP

,

Databases Miscellaneous

,

Oracle Database

Participating Experts
2
Points
500
Comments
4

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Answers

 

by: sujith80Posted on 2007-07-10 at 04:50:23ID: 19452548

It is perfectly fine, and a fact with 40 attributes is relatively small.

For the Date and Time dimensions you have listed above: You can have synonyms in the database which points to the same underlying table. It will help you to logically separate the dimensions, and will be easier while reporting.

The idea of re-using the dimensions reduces the number of dimension tables; hence the dimension maintenance becomes easier.

 

by: rbrookerPosted on 2007-07-10 at 13:50:56ID: 19457645

in our datawarehouse here we have some very wide fact tables. 40 attributes sounds more than agreeable.
we have taken a different tack with the dimensions, for all 6 of your date and time fields there would be a dimension on date and one on time.  we do not use synonyms, but aliases in the queries.

of the 2 options, there is maintenance in the first with managing synonyms, and maintenance in the second with hairy queries.

which path do you wish to go down?

good luck :)

 

by: andy_routledgePosted on 2007-07-11 at 04:02:31ID: 19461282

Thanks guys

I'm going to use views to emulate synonyms, just needed to check that my fact table isnt out of control as all the examples online and in books only contain a few attributes and are described as thin and long as apposed to dimensions which are short and fat.

 

by: sujith80Posted on 2007-07-11 at 23:28:22ID: 19469252

I believe that, you cannot use views here. Reason is you cannot have the PK/FKs defined on the views to link to your fact table.

You may have Materialized views instead(At the cost of refreshing and maintaining the MVs). Considering these synonyms looks like an easier solution.

20120131-EE-VQP-002

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