openjpa-project/src/doc/manual/jpa_overview_intro.xml

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<chapter id="jpa_overview_intro">
    <title>
        Introduction
    </title>
    <para>
    <indexterm>
        <primary>
            EJB3 Persistence
        </primary>
        <see>
            JPA
        </see>
    </indexterm>
    <indexterm>
        <primary>
            JPA
        </primary>
    </indexterm>
The Java Persistence API (JPA) is a specification from
Sun Microsystems for the persistence of Java objects to any relational
datastore. JPA requires J2SE 1.5 (also referred to as "Java 5") or
higher, as it makes heavy use of new Java language features such as annotations
and generics. This document provides an overview of JPA. Unless
otherwise noted, the information presented applies to all JPA implementations.
    </para>
    <note>
        <para>
For coverage of OpenJPA's many extensions to the JPA specification,
see the <link linkend="ref_guide_intro">Reference Guide</link>.
        </para>
    </note>
    <section id="jpa_overview_intro_audience">
        <title>
            Intended Audience
        </title>
        <para>
This document is intended for developers who want to learn about JPA
in order to use it in their applications. It assumes that you have a strong
knowledge of object-oriented concepts and Java, including Java 5 annotations and
generics. It also assumes some experience with relational databases and the
Structured Query Language (SQL).
        </para>
    </section>
    <section id="jpa_overview_intro_transpers">
        <title>
            Lightweight Persistence
        </title>
        <indexterm zone="jpa_overview_intro_transpers">
            <primary>
                lightweight persistence
            </primary>
        </indexterm>
        <para>
        <indexterm>
            <primary>
                persistent data
            </primary>
        </indexterm>
<emphasis>Persistent data</emphasis> is information that can outlive the program
that creates it. The majority of complex programs use persistent data: GUI
applications need to store user preferences across program invocations, web
applications track user movements and orders over long periods of time, etc.
        </para>
        <para>
<emphasis>Lightweight persistence</emphasis> is the storage and retrieval of
persistent data with little or no work from you, the developer. For example,
Java serialization
        <indexterm>
            <primary>
                serialization
            </primary>
        </indexterm>
is a form of lightweight persistence because it can be used to persist Java
objects directly to a file with very little effort. Serialization's capabilities
as a lightweight persistence mechanism pale in comparison to those provided by
JPA, however. The next chapter compares JPA to serialization and other available
persistence mechanisms.
        </para>
    </section>
</chapter>