Database connection
A Database Connection is the method in computer science that allows client software to talk to database server software, whether these exist on the same machine or not. A connection is required to send commands and receive answers, usually in the form of a result set.
Connections are a key concept in data-centric programming, so much so that connection pooling was invented to simplify the process and improve performance. No command can be performed against a database without an "open and available" connection to it.
Connections are built by supplying an underlying driver or provider with a connection string, which is a way of addressing a specific database or server. ( Example: Server=sql_box;Database=Common;User ID=uid;Pwd=password; ) Once a connection has been built, it can be opened and closed at will, and properties ( such as the command timeout length, or transaction, if one exists ) can be set.
Many databases ( such as SQL Server 2000 ) only allow one operation at a time to be performed on a connection. In other words, if a request for data ( a SQL Select statement ) is sent to the database, and a result set is returned, the connection is open, but not available, until the client finishes consuming the result set. Other databases don't impose this limitation.