Design of a data warehouse with more than one fact tables

Question

I\'m new to data warehousing. First, I want to precise than my copy of The Data Warehouse Toolkit is on it\'s way to my mailbox (snail mail :P). But I\'m already studying al

Answer 1

Taking your questions backwards.

A data warehouse can have more than one fact table. However, you do want to minimize joins between fact tables. It's ok to duplicate fact information in different fact tables.

Of the objects you mentioned:

Refund is a fact. Timestamp is the dimension of the refund fact.

Subscription fee is a fact. Timestamp is the dimension of the subscription fee fact.

A refund can happen more than once. I'm guessing that each customer has one subscription fee. So it appears we have two fact tables so far, customer, and customer refund.

If you knew that there could only be at the most 3 refunds (as an example), then you would eliminate the customer refund fact table, and put 3 refund columns in the customer table.

You also mention insurance. A customer can have more than one policy. So we have a third fact table.

A data warehouse is usually designed using a star schema. The star schema is basically one fact table connected to one or more dimension tables. You'll probably have more than one star in a data warehouse, since we already defined 3 fact tables.