Can you give an overview of ADO.NET architecture?

The most important part  in the ADO.NET architecture is the "Data Provider". The  Data Provider provides access to the datasource ( ACCESS, ORACLE, SQL SERVER).In brief  it gives the object to achieve functionalities such as  opening and closing connection, update data and retrieve data . In the below shown figure you can see the 4 main parts of a data provider :-

• Connection.
• Command object (This is the responsible object to use the stored procedures).
• Data Adapter (This object acts as a bridge between the datastore and the dataset).
• Datareader (This object reads data from the data store in only the forward  mode).

The Dataset object shows the disconnected and cached data. If you see the diagram it is not in the direct connection with the data store (ORACLE, SQL SERVER etc) rather it talks with the Data adapter, who is responsible for filling the dataset.  The Dataset can have one or more Data table and relations.