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166 lines
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<meta name="DC.Title" content="iSeries source to System/36 target considerations for DDM" />
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<meta name="abstract" content="When an iSeries server is using DDM to communicate as a source server to access files on a System/36 target server, the information in this topic applies and should be considered." />
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<meta name="description" content="When an iSeries server is using DDM to communicate as a source server to access files on a System/36 target server, the information in this topic applies and should be considered." />
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<meta name="DC.subject" content="target DDM (TDDM), System/36, TDDM (target DDM), DDM target considerations, source DDM (SDDM), server, iSeries, SDDM (source DDM), DDM source considerations, as source, system, AS/400, deleted records, file, extensions, sequential file, extension support, ILE COBOL programming language, extending, ILE RPG programming language, indexed, sequential processing," />
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<meta name="keywords" content="target DDM (TDDM), System/36, TDDM (target DDM), DDM target considerations, source DDM (SDDM), server, iSeries, SDDM (source DDM), DDM source considerations, as source, system, AS/400, deleted records, file, extensions, sequential file, extension support, ILE COBOL programming language, extending, ILE RPG programming language, indexed, sequential processing," />
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<title>iSeries source to System/36 target considerations for DDM</title>
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<body id="rbae5considerations"><a name="rbae5considerations"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1"><span class="keyword">iSeries</span> source to <span class="keyword">System/36</span> target considerations for DDM</h1>
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<div><p>When an <span class="keyword">iSeries™ server</span> is
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using DDM to communicate as a source server to access files on a <span class="keyword">System/36™</span> target server, the information
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in this topic applies and should be considered.</p>
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<div class="section"><ul><li>Some file operations that are not rejected by a target <span class="keyword">iSeries server</span> might
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be rejected by a target <span class="keyword">System/36</span>.
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Examples are: <ul><li>A delete record operation is rejected if the <span class="keyword">System/36</span> file
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is not a delete-capable file. To the <span class="keyword">iSeries</span> source
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user, the rejection might appear to occur for unknown reasons.</li>
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<li>Change operation that attempts to change the key in the primary index
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of a <span class="keyword">System/36</span> file is always
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rejected.</li>
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</ul>
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</li>
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<li>In the <span class="keyword">System/36</span> environment,
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when <span class="keyword">System/36</span> users try to
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copy a delete-capable file to a file that is not delete-capable with the NOREORG
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parameter, a warning message is issued stating that deleted records might
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be copied. The user can choose option 0 (Continue) to continue the process.
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By selecting this option, the file is copied and any deleted records in the
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input file become active records in the output file. An <span class="keyword">iSeries server</span> rejects
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the copy request if the user specifies COMPRESS(*NO).</li>
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<li>If data is copied to a target <span class="keyword">System/36</span> file
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that is a direct file and is not delete-capable, default values
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for all <span class="cmdname">Copy File (CPYF)</span> command parameters except FROMMBR,
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TOMBR, and MBROPT must be specified.</li>
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<li>An <span class="keyword">iSeries server</span> does not support
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the overwriting of data on the Delete File (DLTF) command. If an <span class="keyword">iSeries</span> user accessing a <span class="keyword">System/36</span> wants
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to overwrite the data, an application program must be written on the <span class="keyword">iSeries server</span>, or the user must access the
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target <span class="keyword">System/36</span> and perform
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the overwrite operation.</li>
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<li>Depending on how a <span class="keyword">System/36</span> file
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is originally created, the maximum number of records it can contain is approximately
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eight million. This number can be significantly smaller if the file is not
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extendable or if sufficient storage space is not available to extend the file
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to add more records.</li>
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<li><span class="keyword">System/36</span> supports a maximum
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of three key definitions for logical files and one key definition for keyed
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physical files.</li>
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<li><span class="keyword">System/36</span> file support does
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not allow a file with active logical files to be cleared. When some <span class="keyword">iSeries</span> programs (like ILE COBOL programs)
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open a file for output only, a command to clear the file is issued. A target <span class="keyword">System/36</span> rejects any such command to
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clear the file if a logical file exists over the file to be cleared.</li>
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<li><span class="keyword">System/36</span> file support automatically
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skips deleted records. If an <span class="keyword">iSeries</span> source
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user wishes to change the records in a <span class="keyword">System/36</span> base
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file over which at least one logical file has been built, the file must be
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opened in I/O mode, specifying direct organization and random access by record
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number. Then each record can be read by record number and changed. If a deleted
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record is found, a record-not-found indication is returned, and the record
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might be written rather than rewritten for that position (write operation
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rather than a change operation).</li>
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<li>System/36 file
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support also handles file extensions differently, depending on the file type
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and the language being used. However, an <span class="keyword">iSeries</span> user
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cannot extend any type of <span class="keyword">System/36</span> file
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unless the access method used to access the file is similar to the method
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used when the file was created. <p>If an <span class="keyword">iSeries</span> user
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is accessing a <span class="keyword">System/36</span> file
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with an access method similar to the one used to create the file, the file
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can be extended during its use in the following manner: </p>
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<ul><li>If the file was created as a <em>sequential</em> file, the <span class="keyword">iSeries</span> user
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should, if the <span class="keyword">iSeries</span> language
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is: <ul><li>ILE COBOL programming language: open the file using the EXTEND option.</li>
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<li>PL/I: open the file using the UPDATE option. Perform a read operation
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using the POSITION option of LAST, and then perform the write operations.</li>
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</ul>
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</li>
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</ul>
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<p>(BASIC and ILE RPG programming language both handle any needed file
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extensions automatically.)</p>
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</li>
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<li>If the file was created as a <em>direct</em> file, the <span class="keyword">iSeries</span> user
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should, if the <span class="keyword">iSeries</span> language
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is: <ul><li>ILE COBOL programming language: open the file using the I-O option, position
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the end of file pointer to the end of the file (using, for example, READ LAST),
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and perform a write operation.</li>
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<li>PL/I: open the file using the UPDATE option, position the end of file
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(EOF) pointer to the end of the file (using, for example, READ LAST), and
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perform a write operation. <p>(BASIC and ILE RPG programming language both
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handle any needed file extensions automatically.)</p>
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</li>
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<li>If the file was created as an <em>indexed</em> file, the file is extended
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each time a write operation is performed for a record having a key that does
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not already exist in the file.</li>
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</ul>
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</li>
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<li> The <span class="keyword">iSeries</span> user can access
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sequential <span class="keyword">System/36</span> files using
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either sequential or direct (by relative record number) methods, but significant
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differences occur when EOF or end of data occurs. If a <span class="keyword">System/36</span> sequential
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file is being processed using relative record number access and is opened
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for either input/output or output only, then, on reaching the end of active
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records (EOF), you cannot add new records in the available free space beyond
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the end of data. You will have to close and reopen the file to extend it.
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To extend the file, you can either reopen it as a sequential file or open
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a logical file that uses this file as the base file.</li>
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<li>Because the normal access method used for a <span class="keyword">System/36</span> file
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can be changed by <span class="keyword">iSeries</span> parameters
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to values other than *RMTFILE, it is possible that DDM might attempt to access
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the <span class="keyword">System/36</span> file in ways that
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the <span class="keyword">System/36</span> might not support.
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Normally, the default value (*RMTFILE) on the ACCMTH parameter gives the user
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the needed method of access. The use of access methods not normally expected
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(such as direct or sequential access to indexed files, or sequential access
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to direct files) requires the use of an ACCMTH parameter explicitly for the
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access. <p>The normal access method used for a <span class="keyword">System/36</span> file
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can be changed on the <span class="keyword">iSeries server</span>:
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by the ACCMTH parameter of the DDM file commands <span class="cmdname">Create DDM File
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(CRTDDMF)</span> and <span class="cmdname">Change DDM File (CHGDDMF)</span>, by the
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SEQONLY parameter of the <span class="cmdname">Override with Database File (OVRDBF)</span> command,
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or by using the <span class="cmdname">OVRDBF</span> command to override one DDM file
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with another DDM file having a different ACCMTH value in effect.</p>
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</li>
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<li>The <span class="keyword">iSeries</span> user can access
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a <span class="keyword">System/36</span> file using a member
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name if the member name is *FIRST, or in some cases *LAST, or if the file
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name is the same as the member name.</li>
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<li>Target <span class="keyword">System/36</span> DDM cannot
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support creating logical files with duplicate (nonunique) keys, because the <span class="keyword">System/36</span> local data management key sort
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sends messages to the target server console with options 1 or 3 when duplicate
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keys are detected. This forces the target system operator either to change
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the file attributes to allow duplicate keys or to cancel the target data manager.
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<div class="note"><span class="notetitle">Note:</span> Never cancel the target data manager using a SYSLOG HALT.</div>
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</li>
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</ul>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbae5source36.htm" title="Before an iSeries server can access files on a System/36, Level 1.0 of the DDM architecture must be installed on the System/36. These topics contain information that applies when an iSeries server is the source or target server communicating with a System/36.">System/36 source and target considerations for DDM</a></div>
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</div>
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</div>
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</body>
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