Warehouse and reporting tools

Having completeted the training on siebel analytics, started bulding a data warehouse for a small business case. What is this data warehouse? How is it different from traditinal database systems? Data warehouse as name suggets holds data. If that is to be believed, can my database be replaced with a warehouse? These were some of the questions that I had.
Warehouse holds data but it is different from traditional transactional database systems(DBS). Some of the problems that you have with your transactional database systems are addressed by implementing data warehouse. Normalised data means complex design, relations among different entities causing poor response time, and space constraints are major concerns with a transactional system. In my case, warehouse is implemented to build a decision support system(DSS).
Who needs to have a DSS with real time data? DSS are generally designed to generate reports that are not absolutely live but relatively live. Data warehouse is designed to access multiple data sources, get different dimensions into a FACT table and get the detailed values of each dimension into the corresponding dimension table. Tools used for this purpose should be able to access multiple data sources through different connectors, transform the data if required and push it to a single database. This data that is transformed is used by reporting tools like siebel Analytics and Crystal reports. All in all, it is not the reporting tool that is to be appreciated but the data model in the warehouse that is to be appreciated if at all the reports facilitate the management to make decisions.