72 lines
5.1 KiB
HTML
72 lines
5.1 KiB
HTML
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="How database files are described" />
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<meta name="abstract" content="This topic discusses the ways to describe records in database files." />
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<title>How database files are described</title>
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<body id="rbafodeffi"><a name="rbafodeffi"><!-- --></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">How database files are described</h1>
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<div><p>This topic discusses the ways to describe records in database files.</p>
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<div class="p">Records in database files can be described in two ways: <ul><li>Field-level description. The fields in the record are described to the
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system. Some of the things you can describe for each field include: name,
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length, data type, validity checks, and text description. Database files that
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are created with field-level descriptions are referred to as
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externally described files.</li>
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<li>Record-level description. Only the length of the record in the file is
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described to the system. The system does <em>not</em> know about fields in the
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file. These database files are referred to as program-described files.</li>
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</ul>
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</div>
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<p>Whether a file is described to the field or record level, you must describe
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and create the file before you can compile a program that uses that file.
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That is, the file must exist on the system before you use it.</p>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rbafoxpdd.htm">Externally and program-described data</a></strong><br />
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Programs can use either externally described or program-described files.</li>
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<li class="ulchildlink"><strong><a href="rbafodictdta.htm">Dictionary-described data</a></strong><br />
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Either a program-described file or an externally described file can be defined with the record format descriptions stored in the data dictionary.</li>
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<li class="ulchildlink"><strong><a href="rbaforecft.htm">Record format description</a></strong><br />
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When you describe a database file to the system, you describe the two major parts of the file: the record format and the access path. The record format describes the order of the fields in each record.</li>
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<li class="ulchildlink"><strong><a href="rbafoapd.htm">Access path description</a></strong><br />
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When you describe a database file to the system, you describe the two major parts of the file: the record format and the access path. An access path describes the order in which records are to be retrieved. So when you describe an access path, you describe whether it will be a keyed sequence or arrival sequence access path.</li>
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<li class="ulchildlink"><strong><a href="rbafonamer.htm">Naming conventions used in a database file</a></strong><br />
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The file name, record format name, and field name can be as long as 10 characters and must follow all system naming conventions. Some high-level languages have more restrictive naming conventions than the system does.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rbafodbfcon.htm" title="These topics provide some of the basic database concepts for setting up or working with IBM i5/OS database files.">Database file concepts</a></div>
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