System.InvalidOperationException

The exception that is thrown when a method call is invalid for the object's current state.

It inherits from System.SystemException.

It has many child exceptions, such as System.Net.WebException.

Relational Databases

Thanks to Edgar Codd

Relational databases are built on the concept of relations, which are basically tables. Another way of explaining what a relation is, is a row/column format for storing information. The relational database was first defined in 1970 by Edgar Codd of the IBM San Jose Research Lab (first West Coast research lab for IBM).

Tuples, Attributes and Relations

In the jargon of relational databases, a tuple is a row, an attribute name is a column name, a relation is a table (a set of tuples with the same attributes).

More mscorlib: System.WeakReference

System.WeakReference references an object while still allowing it to be GC'ed.