ibm-information-center/dist/eclipse/plugins/i5OS.ic.ddm_5.4.0.1/rbae5partsddm.htm

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<h1 class="topictitle1">Parts of DDM: Source DDM</h1>
<div><p>The support on the source (or local) <span class="keyword">iSeries™ server</span> is
started, as needed, within a source job to do DDM functions.</p>
<p>The source DDM (SDDM) translates requests for remote file
access from source server application programs into DDM requests that are
routed to the target server for processing. The SDDM support establishes and
manages a DDM conversation with the target server that has the desired remote
file.</p>
<p>When an application program first attempts to access a remote file, a search
for the requested DDM file is done on the source server. As with local file
processing, if the file name is not qualified with a library name, the current
library list for the job in which the program is running is searched for the
specified file. When the file is found, the server accesses the file, determines
that it is a DDM file and starts the SDDM.</p>
<p>When the SDDM is started, it checks to see if a DDM conversation is already
active between the source job starting the SDDM and the target server identified
by the remote location and mode values in the DDM file. If a conversation
that can be used exists, it is used. If not, a program start request is issued
to the appropriate target server to start a TDDM (a target job) on the target
server to establish a DDM conversation between the SDDM and TDDM. Parameters
that are automatically created from information in the DDM file about the
remote file are passed when the remote server sends a program start request.</p>
<p>After the TDDM is started, the SDDM can forward each program request to
the target job for processing. If, for example, input/output (I/O) operations
are to be done on a remote file, the program opens the file and then issues
the desired operation requests. The SDDM forwards the open request and the
TDDM opens the remote file. Then the SDDM forwards each file operation request
to the TDDM, and both of them handle the interchange of data between the application
program and the remote file. When a DDM function is being processed, the requesting
program waits for the function to be completed and the results to be received,
just as it does for local file operations.</p>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="rbae5partsofddm.htm" title="DDM consists of several parts to handle remote file processing among the systems using DDM.">Parts of DDM</a></div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
<div><a href="rbae5xs3xsrc.htm" title="When an application program or user in a source server job first refers to a DDM file, several actions occur as part of processing the request on the source server.">iSeries server as the source server for DDM</a></div>
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