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From an...@apache.org
Subject svn commit: r581221 - /db/jdo/site/xdocs/why_jdo.xml
Date Tue, 02 Oct 2007 13:03:16 GMT
Author: andyj
Date: Tue Oct  2 06:03:16 2007
New Revision: 581221

URL: http://svn.apache.org/viewvc?rev=581221&view=rev
Log: (empty)

Added:
    db/jdo/site/xdocs/why_jdo.xml

Added: db/jdo/site/xdocs/why_jdo.xml
URL: http://svn.apache.org/viewvc/db/jdo/site/xdocs/why_jdo.xml?rev=581221&view=auto
==============================================================================
--- db/jdo/site/xdocs/why_jdo.xml (added)
+++ db/jdo/site/xdocs/why_jdo.xml Tue Oct  2 06:03:16 2007
@@ -0,0 +1,156 @@
+<?xml version="1.0" encoding="iso-8859-1"?>
+<document>
+    <properties>
+        <title>Why JDO ?</title>
+    </properties>
+
+    <body>
+        <section name="Why JDO ?">
+            <p>
+                The majority of applications need to persist (or store) data during their
lifecycle. There are many ways of doing 
+                this with an application written in Java. 
+            </p>
+            <p>
+                You can handle the persistence (and retrieval) of data yourself using <B>JDBC</B>.
With <B>JDBC</B>, you have the burden
+                of having to write the persistence layer yourself. This gives much control,
but also creates significant work, both in 
+                writing the code but also in testing and maintenance.
+            </p>
+            <p>
+                You could also use <B>J2EE</B>, and persist data using Entity
Beans. With <B>J2EE</B> you hand off the persistence of 
+                your objects to the EJB part of the J2EE server. This simplifies things,
but places a major restriction on your code 
+                in that you have to write your objects as Entity Beans. In addition J2EE
adds layers that are not necessarily required 
+                for your application.
+            </p>
+            <p>
+                You can use a proprietary or non-standards compliant persistence framework
like <B>TopLink</B>, or <B>Hibernate</B> and 
+                persist your plain old Java objects. You will, however, be tied in to their
API and be unable to easily move your system 
+                to an alternative implementation.
+            </p>
+            <p>
+                Alternatively you can use <B>JDO</B>, a standardised persistence
interface. With <B>JDO</B> you can take your plain 
+                old Java objects and just persist them as they are. It is totally transparent
and very little work is required by 
+                the developer.
+            </p>
+            <p>
+                To give a <I>guide</I>, here are a few important consideration
points when choosing a persistence layer for your application.
+            </p>
+
+            <table>
+                <tr>
+                    <th>Feature</th>
+                    <th>JDBC</th>
+                    <th>Custom O/R (1)</th>
+                    <th>EJB (2)</th>
+                    <th>JDO</th>
+                    <th>JPA</th>
+                </tr>
+                <tr>
+                    <td>Standards-Driven and Portable</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Choice of datastores</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                </tr>
+                <tr>
+                    <td>Simple Java objects</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Out of box implementation (3)</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Usable in stand-alone application</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Usable in J2EE environment</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Simple to unit test</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Dynamic queries</td>
+                    <td>Yes (4)</td>
+                    <td>Yes</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Primary Key generation</td>
+                    <td>Yes (4)</td>
+                    <td>Yes</td>
+                    <td>No (5)</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Supports inherited objects</td>
+                    <td>Yes (4)</td>
+                    <td>Yes</td>
+                    <td>No (5)</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+                <tr>
+                    <td>Automatic Creation of schema (top-down)</td>
+                    <td>No</td>
+                    <td>Yes</td>
+                    <td>No (5)</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>                
+                <tr>
+                    <td>Supports existing schema (bottom-up)</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                    <td>Yes</td>
+                </tr>
+            </table>
+            <ol>
+                <li>refers to products such as Hibernate, TopLink which follow no standard.</li>
+                <li>refers to entity beans for EJB 2.*</li>
+                <li>refers to whether it is necessary to write the persistence yourself
(e.g as with JDBC) or whether you can just 
+                    persist by simple calls.</li>
+                <li>requires the developer to write this layer.</li>
+                <li>some advanced EJB containers like Bea Weblogic and IBM Websphere
provide support for primary key generation, 
+                    inherited objects and database schema creation as well.</li>
+            </ol>
+        </section>
+
+    </body>
+</document>



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