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<h1 class="topictitle1">Example: Use the basic concepts of DDM in an APPC network</h1>
<div><p>This topic presents a sample application that uses DDM to access
a remote file.</p>
<div class="section"><p>The application can be run by a company that has warehouses located
in several cities. The following figure illustrates the relationships
among the primary items included in a DDM file.</p>
</div>
<div class="section"><p>On an <span class="keyword">iSeries™ server</span> in
Chicago, an <span class="cmdname">Open Database File (OPNDBF)</span> command requests
that file CUST021 be opened for input. Because the file name was not qualified
on the command, the library list for the source job is used to find the file,
which is stored in the NYCLIB library.</p>
</div>
<div class="section"><p>Because CUST021 is a DDM file, the SDDM on the CHICAGO server
is started in the source job when the file is opened. The SDDM uses the remote
location and mode names (NEWYORK and MODENYC) from the DDM file to establish
a DDM conversation with and start a target job (TDDM) on the appropriate target
server (NEWYORK). The remote file to be accessed by the source server program
is CUSTMAST in library XYZ.</p>
</div>
<div class="section"><p>The TDDM receives the remote file name from the SDDM and then
allocates and opens the file named CUSTMAST, which corresponds to the DDM
file named CUST021 on the source server.</p>
</div>
<div class="example"> <div class="fignone" id="rbae5dirrel1__rbae5abc"><a name="rbae5dirrel1__rbae5abc"><!-- --></a><span class="figcap">Figure 1. Relationships among DDM
file parameters and the systems</span><br /><img src="rsll104.gif" alt="The contents of the figure are explained in the text of this section." /><br /></div>
</div>
<div class="section"><p>The remote location name in the DDM file identifies the remote
server where the file exists. The local server uses the remote location name
as well as other values specified in the DDM file to select a device description.
The device description can be either manually created or, if APPN is being
used, automatically created and activated by the server. The SDDM establishes
a DDM conversation with the target server using the values NEWYORK and MODENYC
in the APPC remote location name. The APPC-related support must have been
started on the target server before the request is issued by the SDDM. (No
special support is required on the source server.)</p>
</div>
<div class="section"> <div class="note"><span class="notetitle">Note:</span> The APPN parameter on the <span class="cmdname">Create Controller Description
(APPC) (CRTCTLAPPC)</span> and <span class="cmdname">Create Controller Description (SNA
Host) (CRTCTLHOST)</span> commands determines whether the APPN support
is used. </div>
</div>
</div>
<div>
<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbae5partfile.htm" title="A system object with type *FILE exists on the source server to identify a remote file. It combines the characteristics of a device file and a database file. As a device file, the DDM file refers to a remote location name, local location name, device name, mode, and a remote network ID to identify a remote server as the target server. The DDM file appears to the application program as a database file and serves as the access device between a source server program and a remote file.">Parts of DDM: DDM file</a></div>
</div>
<div class="relconcepts"><strong>Related concepts</strong><br />
<div><a href="../rzahj/rzahjovr.htm">APPC, APPN, and HPR</a></div>
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