You can use any standard databases like SQL Server, Oracle, DB2, Informix, MySql, MS Access etc. You can connect to his databases by using ODBC or OLEDB connections. (You can check help file for CONNECT statment).
You can fetch data from database by writing select queries and then store that table info into qvd by using STORE command in Qlikview. (You can check help file for STOREstatment).
Qlikview supports both Star and Snowflake schema, but in my view Star Schema is the best option, because it reduces the number of joins during runtime.
From QlikView you can read from any of teh databases as Jagan has mentioned. Once you do the reading you will store the data in to .QVD files. The QVD file is also called as an QlikView Database. The Data Modelling in QlikView sed is Dimensional Modelling. The Schema preferred is Star Schema, in some cases you would have a Snow Flake Schema. This would give you optimal performance since the way QlikView stores data for repetitions is in an optimal way. Hope my reply is helpful.