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Discovering SQL: A Hands-On Guide for Beginners by Alex Kriegel

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OBJECT-RELATIONAL MAPPING FRAMEWORKS

Object-relational mapping (ORM) is a way to bridge two inherently different world views. The OOP languages model their world in terms of objects, properties, and methods, while relational databases use entities and relationships, and normalized data models are best suited to store and retrieve scalar values (numbers, character strings). To have an OO client software talking to a relational database means constant translation between the two; at some point, it became obvious that this translation process could be automated, and ORM was born.

There is no shortage of different frameworks created for every technology supporting OO out there, Java, .Net, Deplhi, Groovy, Perl, and Python, to name a few. Currently, the most popular by the number of users in the Java community is the Hibernate 3.0 ORM, with Microsoft developers using NHibernate, LINQ to SQL, and the nascent Microsoft Entity Framework, in no particular order.

Hibernate/NHibernate

Hibernate is an ORM specifically designed and implemented for the Java programming language. It is released as free open source software under the LGP license. The project was started back in 2001 out of frustration with the complexity of EJB, then the hottest environment for constructing enterprise applications. The current implementation, in version 3, is certified for the +Java Persistence API standard. Although being free and open source, it does have an owner, JBossInc, itself owned by Red Hat, which retains ...

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