Use a collection of business objects as the Data Source. When creating an Object Data Source you can select among any available business objects in your solution - for example, Entity Framework models or RIA Services.
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Object Data Source  

Create WCF RIA services applications with reports rendered on the client side. The data must be bound to the report using the Object Data Source and rendered by the Silverlight Report Viewer.
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RIA Services Supported  

Web services are easily used as data sources, letting you render reports without a server counterpart.
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Reports Access Web Services