The document discusses how Silverlight applications work including domain services, metadata, data binding, and validations. Domain services expose business logic from the server to the client. WCF RIA services simplify building multi-tier applications by enabling client and server code sharing. Entities, validations, and other logic can be reused on both tiers. Data binding in Silverlight binds properties and paths on entities to UI elements. Validations can be done client-side or server-side using data annotation attributes.