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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-2D93660B-8206-5D20-85F5-6FFCF4549127" xml:lang="en"><title>Persistent

stores</title><shortdesc>A store is persistent if you can close it, re-open it, and then

gain access to the same data.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>A persistent store has the concept of a root stream. The root stream is,

in effect, the starting point from which all others streams within the store

can be found.</p>

<p>Before closing a persistent store you have created, you must set the ID

of the root stream. After you have opened the persistent store, the first

thing you must do is look up the root stream ID. You can then open the root

stream and start reading data from the store.</p>

<p>Persistent stores are represented by the abstract class <codeph>CPersistentStore</codeph>.

This class, derived from <codeph>CStreamStore</codeph> has the root stream

ID and expands on the abstract framework provided by <codeph>CStreamStore</codeph>,

by adding behaviour for setting and retrieving the root stream ID.</p>

<p>File stores are an example of persistent stores.</p>

<p>The following diagram shows the idea of a persistent store with a root

stream:</p>

<fig id="GUID-8A987703-9602-563A-97D9-6DD6012708C4">

<title>Persistent store with a root stream</title>

<image href="GUID-FD503B6E-889C-521F-B61A-0EBDCA8CD9AC_d0e355285_href.png" placement="inline"/>

</fig>

<section id="GUID-DD8F38F5-503A-46A5-AF28-74A1DE08E867"><title>See also</title> <p><xref href="GUID-C9D8D913-C65F-5A69-A606-30F59BFB38E2.dita">File

stores</xref> </p> </section>