Database connection

In computer science, a database connection is the means by which a database server and its client software communicate with each other. The term is used whether or not the client and the server are on different machines.

The client uses a database connection to send commands to and receive replies from the server. A database is stored as a file or a set of files on magnetic disk or tape, optical disk, or some other secondary storage device. The information in these files may be broken down into records, each of which consists of one or more fields.

Fields are the basic units of data storage, and each field typically contains information pertaining to one aspect or attribute of the entity described by the database. Records are also organized into tables that include information about relationships between its various fields. Although database is applied loosely to any collection of information in computer files, a database in the strict sense provides cross-referencing capabilities.

Connections are a key concept in data-centric programming. Since some DBMSs require considerable time to connect, connection pooling is used to 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 used to address a specific database or server and to provide instance and user authentication credentials (for 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 time-out length, or transaction, if one exists) can be set. The connection string consists of a set of key-value pairs, dictated by the data access interface of the data provider.

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