File-based database asp.net

asp.net sql xml database text

Yes it is: SQLite :)

There is ADO Provider:http://sqlite.phxsoftware.com/forums/default.aspx?GroupID=2

There is article on that:http://www.aspfree.com/c/a/Database/Using-SQLite-for-Simple-Database-Storage/

asp.net sql xml database text

The DataSet from the .NET Framework is also an option. See DataSets, DataTables, and DataViews (ADO.NET) on MSDN.

asp.net sql xml database text

Theoretical:

These projects will give you an idea