System.Data namespace in .NET Framework Class Library
The System.Data namespace consists mostly of the classes that constitute the ADO.NET architecture. The ADO.NET architecture enables developers to build components that efficiently manage data from multiple data sources. In a disconnected scenario, for example where a mobile application client connects to a database, extracts data, and then disconnects, ADO.NET provides the tools to request, update, and reconcile data in multiple tier systems.
The same ADO.NET model can be used in client applications, such as Windows Forms, in Web applications created with ASP.NET, in Web services, in daemon applications, or even in database trigger logic.