dw is also a database but the purpose is for business analysis.

in general a database is a reservior having operational data needed for daily business and they are ever changing. since the new data is always overwriting the old one there is no way to compare the change in data this is wer a dw comes in picture. dw has historical datas and the current data so comparison becomes very easy for business analysis.

ds is a tool for ETL.

ETL tools: informatica, ds junction, abinitio,ds,cognos, etc

reporting: cognos, bo, etc