To store, organize, and retrieve data, most applications use relational databases. Java EE applications access relational databases through the JDBC API.
A JDBC resource (data source) provides applications with a means of connecting to a database. Typically, a JDBC resource is created for each database accessed by the applications deployed in a domain. Transactional access to JDBC resources is available from servlets, JSP pages, and enterprise beans. The connection pooling and distributed transaction features are intended for use by JDBC drivers to coordinate with an application server.
For more information, see DataSource Objects and Connection Pools.