You have a need of data for analysis and reporting.
Whatever the specific reasons are, fundamentally, you, whether you are a technical developer or a business user, need a data warehouse because accessing the data directly from their operational systems (transactional systems) has not been satisfying.
Your dissatisfaction is either because you have difficulty to understand or access, or you get a slow response time, or both. Technically, the problems happen because the operational/transaction systems are not developed for your data access purpose.
A data warehouse is the middleware between the source (the operational/transactional systems) and you. A data warehouse resolves the problems by dedicating its design, implementation and delivery, to serve your analytical data and reporting requirement.
Your data warehouse collects data you need from various sources, integrate, structure, store, and make them available such that you can access them in easy manner, at the time you need, and with your expected response time.
