How is data stored in SAP BW?

Can you extract data from several data cubes in BW and merge them for a report -- or do you have to create a specific data cube for each report requested? What software is used to create the data cubes in BW?

BW provides the necessary tools to create and load data to InfoProviders. BW data is stored in InfoProviders, which are InfoCubes, ODSs and master data objects. Multi-providers or InfoSets can be created to retrieve data from multiple InfoCubes or ODSs.