how to create a data warehouse or data mart

i want to create a data mart from an existing OLTP database. for example northwind or i will create an OLTP database. i dont know how i can create data mart from OLTP database. i want to learn that step by step. help me? please!!There is no step-by-step method for creating data warehouses.
You could try Kimball's one-size-fits-all star schema approach to create a datamart, but I don't hold a high opinon of that.
My recommendation would be read some of the books by Inmon and his associates.|||i read it. but now i have a project. i need simple examples. i saw the nwindmart from the northwind database. but i dont understand how they create it from the northwind.|||Creating a true "data warehouse" is an iterative process that involves both the development team and the end-users. If you have read Inmon's work, then you know that the methodology is to start with a small set of important and related tables, and prune and enhance from there as business needs are determined.
Are you just talking about creating a data cube?|||firstly i must create a simple OLTP database. I will make it like northwind or pubs. then i must create a simple data mart from this OLTP database. this data mart has 4 or 5 dimension. and then i must create a cube that has 3 dimension. i have northwind database and nwindmart. i try to understand that how they create nwindmart from the northwind.

i need simple example for example how can create salesfact table from northwind? they used DTS or ...

i dont read that book exactly. but i read some parts.|||You need to read Books Online and other available documentation, and then come back to the forum with specific questions.