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PrimaryKey (Oracle - Berkeley DB Java API)
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<b>Berkeley DB</b><br><font size="-1"> version 4.7.25</font></EM>
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com.sleepycat.persist.model</FONT>
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Annotation Type PrimaryKey</H2>
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<HR>
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<DL>
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<DT><PRE><FONT SIZE="-1"><A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Documented.html" title="class or interface in java.lang.annotation">@Documented</A>
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<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Retention.html" title="class or interface in java.lang.annotation">@Retention</A>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Retention.html#value()" title="class or interface in java.lang.annotation">value</A>=<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/RetentionPolicy.html#RUNTIME" title="class or interface in java.lang.annotation">RUNTIME</A>)
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<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Target.html" title="class or interface in java.lang.annotation">@Target</A>(<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/Target.html#value()" title="class or interface in java.lang.annotation">value</A>=<A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/annotation/ElementType.html#FIELD" title="class or interface in java.lang.annotation">FIELD</A>)
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</FONT>public @interface <B>PrimaryKey</B></DL>
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</PRE>
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<P>
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Indicates the primary key field of an entity class. The value of the
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primary key field is the unique identifier for the entity in a <A HREF="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><CODE>PrimaryIndex</CODE></A>.
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<p><A HREF="../../../../com/sleepycat/persist/model/PrimaryKey.html" title="annotation in com.sleepycat.persist.model"><CODE>PrimaryKey</CODE></A> may appear on at most one declared field per
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class.</p>
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<p>Primary key values may be automatically assigned as sequential integers
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using a <A HREF="../../../../com/sleepycat/persist/model/PrimaryKey.html#sequence()"><CODE>sequence()</CODE></A>. In this case the type of the key field is
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restricted to a simple integer type.</p>
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<p>A primary key field may not be null, unless it is being assigned from a
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sequence.</p>
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<p><a name="keyTypes"><strong>Key Field Types</strong></a></p>
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<p>The type of a key field must either be one of the following:</p>
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<ul>
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<li>Any of the <a href="Entity.html#simpleTypes">simple
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types</a>.</li>
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<li>A composite key class containing one or more simple type fields.</li>
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</ul>
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<p>Enum types and array types are not allowed.</p>
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<p>When using a composite key class containing more than one key field, each
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field of the composite key class must be annotated with <A HREF="../../../../com/sleepycat/persist/model/KeyField.html" title="annotation in com.sleepycat.persist.model"><CODE>KeyField</CODE></A> to
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identify the storage order and default sort order. See <A HREF="../../../../com/sleepycat/persist/model/KeyField.html" title="annotation in com.sleepycat.persist.model"><CODE>KeyField</CODE></A> for
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an example and more information on composite keys.</p>
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<p><a name="sortOrder"><strong>Key Sort Order</strong></a></p>
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<p>Key field types, being simple types, have a well defined and reasonable
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default sort order, described below. This sort order is based on a storage
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encoding that allows a fast byte-by-byte comparison.</p>
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<ul>
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<li>All simple types except for <code>String</code> are encoded so that they are
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sorted as expected, that is, as if the <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Comparable.html#compareTo(T)" title="class or interface in java.lang"><CODE>Comparable.compareTo(T)</CODE></A> method
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of their class (or, for primitives, their wrapper class) is called.</li>
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<br>
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<li>Strings are encoded as UTF-8 byte arrays. Zero (0x0000) character
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values are UTF encoded as non-zero values, and therefore embedded zeros in
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the string are supported. The sequence {0xC0,0x80} is used to
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encode a zero character. This UTF encoding is the same one used by native
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Java UTF libraries. However, this encoding of zero does impact the
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lexicographical ordering, and zeros will not be sorted first (the natural
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order) or last. For all character values other than zero, the default UTF
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byte ordering is the same as the Unicode lexicographical character
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ordering.</li>
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</ul>
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<p>To override the default sort order, you can use a composite key class
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that implements <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Comparable.html" title="class or interface in java.lang"><CODE>Comparable</CODE></A>. This allows overriding the sort order
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and is therefore useful even when there is only one key field in the
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composite key class. See <a href="KeyField.html#comparable">Custom
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Sort Order</a> for more information on sorting of composite keys.</p>
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<p><a name="inherit"><strong>Inherited Primary Key</strong></a></p>
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<p>If it does not appear on a declared field in the entity class, <code>PrimaryKey</code> must appear on a field of an entity superclass. In the
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following example, the primary key on the base class is used:</p>
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<pre class="code">
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@Persistent
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class BaseClass {
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@PrimaryKey
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long id;
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...
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}
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@Entity
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class Employee extends BaseClass {
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// inherits id primary key
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...
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}</pre>
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<p>If more than one class with <code>PrimaryKey</code> is present in a class
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hierarchy, the key in the most derived class is used. In this case, primary
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key fields in superclasses are "shadowed" and are not persistent. In the
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following example, the primary key in the base class is not used and is not
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persistent:</p>
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<pre class="code">
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@Persistent
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class BaseClass {
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@PrimaryKey
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long id;
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...
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}
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@Entity
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class Employee extends BaseClass {
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// overrides id primary key
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@PrimaryKey
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String uuid;
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...
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}</pre>
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<p>Note that a <code>PrimaryKey</code> is not allowed on entity subclasses. The
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following is illegal and will cause an <code>IllegalArgumentException</code> when
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trying to store an <code>Employee</code> instance:</p>
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<pre class="code">
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@Entity
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class Person {
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@PrimaryKey
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long id;
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...
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}
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@Entity
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class Employee extends Person {
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@PrimaryKey
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String uuid;
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...
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}</pre>
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<P>
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<P>
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<HR>
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<P>
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<!-- =========== ANNOTATION TYPE OPTIONAL MEMBER SUMMARY =========== -->
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<A NAME="annotation_type_optional_element_summary"><!-- --></A>
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<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
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<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
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<B>Optional Element Summary</B></FONT></TH>
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</TR>
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<TR BGCOLOR="white" CLASS="TableRowColor">
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<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
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<CODE> <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A></CODE></FONT></TD>
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<TD><CODE><B><A HREF="../../../../com/sleepycat/persist/model/PrimaryKey.html#sequence()">sequence</A></B></CODE>
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<BR>
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The name of a sequence from which to assign primary key values
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automatically.</TD>
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</TR>
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</TABLE>
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<P>
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<A NAME="sequence()"><!-- --></A><H3>
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sequence</H3>
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<PRE>
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public abstract <A HREF="http://java.sun.com/j2se/1.5.0/docs/api/java/lang/String.html" title="class or interface in java.lang">String</A> <B>sequence</B></PRE>
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<DL>
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<DD>The name of a sequence from which to assign primary key values
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automatically. If a non-empty string is specified, sequential integers
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will be assigned from the named sequence.
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<p>A single sequence may be used for more than one entity class by
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specifying the same sequence name for each <code>PrimaryKey</code>. For
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each named sequence, a <A HREF="../../../../com/sleepycat/db/Sequence.html" title="class in com.sleepycat.db"><CODE>Sequence</CODE></A> will be used to
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assign key values. For more information on configuring sequences, see
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<A HREF="../../../../com/sleepycat/persist/EntityStore.html#setSequenceConfig(java.lang.String, com.sleepycat.db.SequenceConfig)"><CODE>EntityStore.setSequenceConfig</CODE></A>.</p>
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<p>To use a sequence, the type of the key field must be a primitive
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integer type (<code>byte</code>, <code>short</code>, <code>int</code> or <code>long</code>)
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or the primitive wrapper class for one of these types. A composite key
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class may also be used to override sort order, but it may contain only a
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single key field that has one of the types previously mentioned.</p>
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<p>When an entity with a primary key sequence is stored using one of the
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<code>put</code> methods in the <A HREF="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><CODE>PrimaryIndex</CODE></A>, a new key will be
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assigned if the primary key field in the entity instance is null (for a
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reference type) or zero (for a primitive integer type). Specifying zero
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for a primitive integer key field is allowed because the initial value
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of the sequence is one (not zero) by default. If the sequence
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configuration is changed such that zero is part of the sequence, then
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the field type must be a primitive wrapper class and the field value
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must be null to cause a new key to be assigned.</p>
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<p>When one of the <code>put</code> methods in the <A HREF="../../../../com/sleepycat/persist/PrimaryIndex.html" title="class in com.sleepycat.persist"><CODE>PrimaryIndex</CODE></A>
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is called and a new key is assigned, the assigned value is returned to
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the caller via the key field of the entity object that is passed as a
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parameter.</p>
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<P>
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<DD><DL>
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</DL>
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</DD>
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<DD><DL>
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</DL>
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<DL>
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<DT><B>Default:</B><DD>""</DD>
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</DL>
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</DL>
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<TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM>
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<b>Berkeley DB</b><br><font size="-1"> version 4.7.25</font></EM>
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