89 lines
6.5 KiB
HTML
89 lines
6.5 KiB
HTML
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<meta name="DC.Title" content="DDM-related differences between iSeries and System/36 files" />
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<meta name="abstract" content="Because of differences between the types of files supported by an iSeries server and a System/36, several items need to be considered when DDM is used between these two servers." />
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<title>DDM-related differences between iSeries and System/36 files</title>
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<body id="rbae5diff36"><a name="rbae5diff36"><!-- --></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">DDM-related differences between <span class="keyword">iSeries</span> and <span class="keyword">System/36</span> files</h1>
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<div><p>Because of differences between the types of files supported by
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an <span class="keyword">iSeries™ server</span> and a <span class="keyword">System/36™</span>, several items need to be considered
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when DDM is used between these two servers.</p>
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<div class="section"><p> Generally, when a <span class="keyword">System/36</span> file
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is created locally (by the BLDFILE utility, for example), the <span class="keyword">System/36</span> user
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specifies such things as the type of file (S = sequential, D = direct, or
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I = indexed), whether records or blocks are to be allocated, how many of them
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are to be allocated, and how many additional times this amount can be added
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to the file to extend it.</p>
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</div>
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<div class="section"><p> Also, you can specify whether the file is to be <em>delete-capable</em> (DFILE)
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or not (NDFILE). In files specified as <em>not delete-capable</em>, records
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can be added or changed in the file, but not deleted.</p>
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</div>
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<div class="section"><p> Once these attributes have been specified, <span class="keyword">System/36</span> then
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creates the file and fills it with the appropriate hexadecimal characters.
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If a <span class="keyword">System/36</span> user specifies
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the file as:</p>
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<ul><li> A <em>sequential</em> file, the entire file space is filled with hex 00
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characters and the end-of-file (EOF) pointer is set to the beginning of the
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initial extent. If you attempt to read an empty sequential file, an EOF condition
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is received.</li>
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<li>A <em>direct</em> file that is <em>delete-capable</em>, the entire file space
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is filled with hex FF characters (deleted records) and the EOF pointer is
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set to the end of the initial extent. If you attempt to read an empty direct
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file that is delete-capable, a record-not-found condition is received.</li>
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<li>A <em>direct</em> file that is <em>not delete-capable</em>, the entire file
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space is filled with hex 40 characters (blank or null records) and the EOF
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pointer is set to the end of the initial extent. If you attempt to read an
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empty direct file that is not delete-capable, a blank record is returned for
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every record in the file until the end of the file is reached.</li>
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<li> An <em>indexed</em> file, it is prepared in the same manner as sequential
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files.</li>
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</ul>
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</div>
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<div class="section"><p>Typically, once a delete-capable file has been in use, it contains
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a relatively continuous set of active records with only a few deleted records,
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possibly an end of data marker, and then a continuous set of deleted records
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to the end of the file (EOF) space. This means that, unless the file is reorganized,
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a user can <em>un</em>delete (recover) a deleted record.</p>
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</div>
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<div class="section"><p>Of the three types of <span class="keyword">System/36</span> files, <span class="keyword">System/36</span> indexed files differ little
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from <span class="keyword">iSeries</span>-supported logical
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files. If an <span class="keyword">iSeries</span> source
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program is to use DDM to access the other types of files on a <span class="keyword">System/36</span>,
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the <span class="keyword">iSeries</span> application programmer
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should first consider the items remaining in this topic selection that
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relate to <span class="keyword">System/36</span>.</p>
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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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</html> |