What is ORM ?

Object Relational Mapping(ORM) is a technique/solution that provides an object-based view of data to applications which it can manipulate.The basic purpose of ORM is to allow an application written in an object oriented language to deal with the information it manipulates in terms of objects, rather than in terms of database-specific concepts such as rows, columns and tables.

In the Java world, ORM's first appearance was under the form of entity beans. But entity beans have limited scope in Java EE domain,they can not be exploited for Java SE based applications.The mapping of class lever attributes is done to table columns.For example a String variabe of a class will directly map onto a VARCHAR column. A relationship mapping is the one that you use when you have an attribute of a class that holds a reference to an instance of some other class in your domain model. The most common types of relationship mappings are "one to one", "one to many" or "many to many".