81 lines
5.1 KiB
HTML
81 lines
5.1 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Externally and program-described data" />
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<meta name="abstract" content="Programs can use either externally described or program-described files." />
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<meta name="description" content="Programs can use either externally described or program-described files." />
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<meta name="DC.Relation" scheme="URI" content="rbafodeffi.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rbafoxpdd" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Externally and program-described data</title>
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</head>
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<body id="rbafoxpdd"><a name="rbafoxpdd"><!-- --></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">Externally and program-described data</h1>
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<div><p>Programs can use either externally described or program-described
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files.</p>
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<div class="p">Programs can use file descriptions in two ways: <ul><li>The program uses the field-level descriptions that are part of the file.
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Because the field descriptions are external to the program itself, the data
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is called externally described data.</li>
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<li>The program uses fields that are described in the program itself; therefore,
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the data is called program-described data. Fields in files that are only described
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to the record level must be described in the program using the file.</li>
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</ul>
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</div>
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<p>However, if you choose to describe a file to the field level, the system
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can do more for you. For example, when you compile your programs, the system
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can extract information from an externally described file and automatically
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include field information in your programs. Therefore, you do not have to
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code the field information in each program that uses the file.</p>
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<p>The following figure shows the typical relationships between files and
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programs on the <span class="keyword">iSeries™</span> server:</p>
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<br /><img src="rbafo500.gif" alt="Examples of files" /><br /><dl><dt class="dlterm"><span class="uicontrol">1</span> Externally Described Data</dt>
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<dd>The program uses the field-level description of a file that is defined
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to the system. At compilation time, the language compiler copies the external
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description of the file into the program.</dd>
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<dt class="dlterm"><span class="uicontrol">2</span> Program-Described Data</dt>
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<dd>The program uses a file that is described to the field level to the system,
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but it does not use the actual field descriptions. At compilation time, the
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language compiler does not copy the external description of the file into
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the program. The fields in the file are described in the program. In this
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case, the field attributes (for example, field length) used in the program
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must be the same as the field attributes in the external description.</dd>
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<dt class="dlterm"><span class="uicontrol">3</span> Program-Described Data</dt>
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<dd>The program uses a file that is described only to the record level to
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the system. The fields in the file must be described in the program.</dd>
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</dl>
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<p>Externally described files can also be described in a program. You might
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want to use this method for compatibility with previous systems. For example,
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you want to run programs on the <span class="keyword">iSeries</span> server
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that originally came from a traditional file system. Those programs use program-described
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data, and the file itself is only described to the record level. At a later
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time, you describe the file to the field level (externally described file)
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to use more of the database functions available on the system. Your old programs,
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containing program-described data, can continue to use the externally described
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file while new programs use the field-level descriptions that are part of
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the file. Over time, you can change one or more of your old programs to use
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the field-level descriptions.</p>
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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="rbafodeffi.htm" title="This topic discusses the ways to describe records in database files.">How database files are described</a></div>
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</div>
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</div>
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</body>
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</html>
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