A DataSet is Disconnected Architecture,means their is no need to always open & close connection.it is cache of data retrieved from database.it is made up of collection of datatable.Dataset can be Typed & UnTyped usually,datasets are typed in Visual basic.A typed dataset is dataset which derived from dataset class & uses information in XML schema file(XSD file).An untyped dataset has no built in schema.it can contain tables,column & rows.but those are exposed only as collections