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<td align="left" valign="top"><font face="helvetica, arial, sans-serif"><b>Developing Persistence Architectures Using EclipseLink Database Web Services</b><br />
<b>Release 3.0</b><br />
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<div class="sect1">
<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">Understanding XML-to-Relational Mapping (XRM)</font></h1>
<p>EclipseLink's ORM and OXM features provides the basis for a powerful bridge between a database's relational structure(s) and XML's hierarchical structure.</p>
<div class="figure"><a id="TLDBW111" name="TLDBW111"></a><a id="sthref7" name="sthref7"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Figure 1-1 EclipseLink XR Architecture</font></em></strong></p>
<img src="img/chart_v2.gif" alt="Description of Figure 1-1 follows" title="Description of Figure 1-1 follows" longdesc="img_text/chart_v2.htm" /><br />
<a id="sthref8" name="sthref8" href="img_text/chart_v2.htm">Description of "Figure 1-1 EclipseLink XR Architecture"</a><br />
<br /></div>
<!-- class="figure" -->
<a id="TLDBW112" name="TLDBW112"></a>
<div class="sect2"><a id="sthref9" name="sthref9"></a>
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Configuration</font></h2>
<p>A typical EclipseLink DBWS service is packaged in an archive (<code>.jar</code> or&nbsp;<code>.war</code> file) with a service descriptor file <code>eclipselink-dbws.xml</code> in the <code>META-INF</code> directory (or <code>WEB-INF/classes/META-INF</code> when packaged in a&nbsp;<code>.war</code> file). To bridge the relational database and XML worlds, an EclipseLink <code>sessions.xml</code> (<code>eclipselink-dbws-sessions.xml</code>) points to two Eclipse projects: one for the ORM side, the other for the OXM side. The service also requires an XML Schema Definition file <code>eclipselink-dbws-schema.xsd</code> which in conjunction with the OXM project, specifies how information from the database is to be "shaped" into XML documents.</p>
<div class="figure"><a id="TLDBW113" name="TLDBW113"></a><a id="sthref10" name="sthref10"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Figure 1-2 Typical EclipseLink DBWS Service Files</font></em></strong></p>
<img src="img/dbwsservicepackage.gif" alt="Typical EclipseLink DBWS Service Files" title="Typical EclipseLink DBWS Service Files" longdesc="img_text/dbwsservicepackage.htm" /><br />
<a id="sthref11" name="sthref11" href="img_text/dbwsservicepackage.htm">Description of "Figure 1-2 Typical EclipseLink DBWS Service Files"</a><br />
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<p>The EclipseLink DBWS service descriptor file, <code>eclipselink-dbws.xml</code>, is easy to read, with minimal required information and simple defaults for omitted fields. This allows for auto-generation by a utility or manual editing. <a href="#CJADJDDA">Example 1-1</a> illustrates a sample DBWS service descriptor file.</p>
<div class="example"><a id="CJADJDDA" name="CJADJDDA"></a><a id="TLDBW114" name="TLDBW114"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 1-1 Example DBWS Service descriptor file</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;dbws
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
&gt;
&lt;<strong>name</strong>&gt;example&lt;/<strong>name</strong>&gt;
&lt;<strong>sessions-file</strong>&gt;example-dbws-sessions.xml&lt;/<strong>sessions-file</strong>&gt;
&lt;query&gt;
&lt;name&gt;countEmployees
&lt;result&gt;
&lt;type&gt;xsd:int&lt;/type&gt;
&lt;/result&gt;
&lt;sql&gt;&lt;!--[CDATA[select count(*) from EMP]]--&gt;&lt;/sql&gt;
&lt;/query&gt;
&lt;/dbws&gt;
</pre></div>
<!-- class="example" -->
<p><a href="#CJAHDJAB">Table 1-1</a> describes the elements of the EclipseLink DBWS service descriptor file.</p>
<div class="tblhruleformalwide"><a id="TLDBW115" name="TLDBW115"></a><a id="sthref12" name="sthref12"></a><a id="CJAHDJAB" name="CJAHDJAB"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Table 1-1 EclipseLink DBWS Service Descriptor File Elements</font></em></strong></p>
<table class="HRuleFormalWide" title="EclipseLink DBWS Service Descriptor File Elements" summary="This table describes the EclipseLink DBWS service descriptor file elements. Additionally, it indicates if the element is required and what the default value is." dir="ltr" border="1" width="100%" frame="hsides" rules="rows" cellpadding="3" cellspacing="0">
<col width="21%" />
<col width="23%" />
<col width="25%" />
<col width="*" />
<thead>
<tr align="left" valign="top">
<th align="left" valign="bottom" id="r1c1-t3"><font face="Arial, Helvetica, sans-serif"><strong>Element</strong></font></th>
<th align="left" valign="bottom" id="r1c2-t3"><font face="Arial, Helvetica, sans-serif"><strong>Description</strong></font></th>
<th align="left" valign="bottom" id="r1c3-t3"><font face="Arial, Helvetica, sans-serif"><strong>Required?</strong></font></th>
<th align="left" valign="bottom" id="r1c4-t3"><font face="Arial, Helvetica, sans-serif"><strong>Default</strong></font></th>
</tr>
</thead>
<tbody>
<tr align="left" valign="top">
<td align="left" id="r2c1-t3" headers="r1c1-t3">
<p><code>name</code></p>
</td>
<td align="left" headers="r2c1-t3 r1c2-t3">
<p>Name of the EclipseLink DBWS service.</p>
</td>
<td align="left" headers="r2c1-t3 r1c3-t3">
<p>Yes, set by the <code>projectName</code> property in the <code>DBWSBuilder</code>.</p>
</td>
<td align="left" headers="r2c1-t3 r1c4-t3">
<p>None</p>
</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r3c1-t3" headers="r1c1-t3">
<p><code>sessions-file</code></p>
</td>
<td align="left" headers="r3c1-t3 r1c2-t3">
<p>Name of the EclipseLink <code>sessions.xml</code> file.</p>
</td>
<td align="left" headers="r3c1-t3 r1c3-t3">
<p>No</p>
</td>
<td align="left" headers="r3c1-t3 r1c4-t3">
<p><code>eclipselink-dbws-sessions.xml</code></p>
</td>
</tr>
<tr align="left" valign="top">
<td align="left" id="r4c1-t3" headers="r1c1-t3">
<p>Any of the following:</p>
<ul>
<li>
<p><code>insert</code></p>
</li>
<li>
<p><code>update</code></p>
</li>
<li>
<p><code>delete</code></p>
</li>
<li>
<p><code>query</code></p>
</li>
</ul>
</td>
<td align="left" headers="r4c1-t3 r1c2-t3">
<p>Service operations</p>
</td>
<td align="left" headers="r4c1-t3 r1c3-t3">
<p>At least one operation</p>
</td>
<td align="left" headers="r4c1-t3 r1c4-t3">
<p>None</p>
</td>
</tr>
</tbody>
</table>
<br /></div>
<!-- class="tblhruleformalwide" --></div>
<!-- class="sect2" -->
<a id="TLDBW116" name="TLDBW116"></a>
<div class="sect2"><a id="sthref13" name="sthref13"></a>
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">XML Schema Definition</font></h2>
<p>The EclipseLink DBWS service schema file <code>eclipselink-dbws-schema.xsd</code> can be created by hand, or auto-generated by the design-time <code>DBWSBuilder</code> utility that derives XML element-tag names from Database metadata (column names, types, nullable, and so on).</p>
<p>The DBWSBuilder utility will not generate an XML Schema Definition when the information returned by a query operation has no pre-determined structure, such as:</p>
<ul>
<li>
<p>a <code>resultSet</code> from a custom SQL <strong>query operation</strong></p>
</li>
<li>
<p>the results from a Stored Procedure <strong>query operation</strong></p>
</li>
<li>
<p>the row-count from an <strong>update</strong> <strong>operation</strong></p>
</li>
</ul>
<p>In these cases, the EclipseLink DBWS runtime provider uses information only available at the time of query execution to build the XML document:</p>
<div class="example"><a id="TLDBW117" name="TLDBW117"></a><a id="sthref14" name="sthref14"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 1-2 Example Simple XML Format (SXF) document</font></em></strong></p>
<p>Element tag names are direct copies of table's column names.</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;?xml version = '1.0' encoding = 'UTF-8'?&gt;
&lt;simple-xml-format&gt;
&lt;simple-xml&gt;
&lt;EMPNO&gt;7788&lt;/EMPNO&gt;
&lt;ENAME&gt;SCOTT&lt;/ENAME&gt;
&lt;JOB&gt;ANALYST&lt;/JOB&gt;
&lt;MGR&gt;7566&lt;/MGR&gt;
&lt;HIREDATE&gt;1987-04-19T00:00:00.000-0400&lt;/HIREDATE&gt;
&lt;SAL&gt;3000&lt;/SAL&gt;
&lt;DEPTNO&gt;20&lt;/DEPTNO&gt;
&lt;/simple-xml&gt;
&lt;simple-xml&gt;
&lt;EMPNO&gt;7369&lt;/EMPNO&gt;
&lt;ENAME&gt;SMITH&lt;/ENAME&gt;
&lt;JOB&gt;CLERK&lt;/JOB&gt;
&lt;MGR&gt;7902&lt;/MGR&gt;
&lt;HIREDATE&gt;1980-12-17T00:00:00.000-0400&lt;/HIREDATE&gt;
&lt;SAL&gt;800&lt;/SAL&gt;
&lt;DEPTNO&gt;20&lt;/DEPTNO&gt;
&lt;/simple-xml&gt;
&lt;/simple-xml-format&gt;
</pre>
<p>These XML documents are "dumb," as they cannot be validated against any pre-determined schema - or more accurately, only the following very <em>permissive</em> "sequence-of-any" schema can validate such documents:</p>
</div>
<!-- class="example" -->
<div class="example"><a id="TLDBW118" name="TLDBW118"></a><a id="sthref15" name="sthref15"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 1-3 Simple XML Format Schema</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;xsd:schema
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
&gt;
&lt;xsd:complexType name="simple-xml-format"&gt;
&lt;xsd:sequence&gt;
&lt;xsd:any minOccurs="0"/&gt;
&lt;/xsd:sequence&gt;
&lt;/xsd:complexType&gt;
&lt;/xsd:schema&gt;
</pre>
<p>The element tags <code>simple-xml-forma</code>t and <code>simple-xml</code> can be customized by setting the appropriate properties on an <strong>operation</strong>.</p>
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