82 lines
4.8 KiB
HTML
82 lines
4.8 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.Title" content="Referential integrity terms" />
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<meta name="abstract" content="A discussion of referential integrity requires an understanding of several terms. These terms are in an order that might help you understand their relationship to each other." />
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<meta name="description" content="A discussion of referential integrity requires an understanding of several terms. These terms are in an order that might help you understand their relationship to each other." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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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>Referential integrity terms</title>
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</head>
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<body id="rbaforzahfrcc"><a name="rbaforzahfrcc"><!-- --></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">Referential integrity terms</h1>
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<div><p>A discussion of referential integrity requires an understanding
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of several terms. These terms are in an order that might help you understand
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their relationship to each other. </p>
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<div class="section"><div class="p"><dl><dt class="dlterm">Primary key constraint</dt>
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<dd>A field or set of fields in a database file that must be unique, ascending,
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and cannot contain null values. The primary key is the primary file access
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path. The primary key constraint can be used as the parent key when adding
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a referential constraint. A primary key constraint is really a unique constraint
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with some special attributes.</dd>
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<dt class="dlterm">Unique constraint</dt>
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<dd>A field or set of fields in a database file that must be unique, ascending,
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and can contain null values.</dd>
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<dt class="dlterm">Parent key</dt>
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<dd>A field or set of fields in a database file that must be unique, ascending,
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and might or might not contain null values. The parent key of the parent file
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is used to add a referential constraint to the dependent file. The parent
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key must be either a primary key or a unique constraint.</dd>
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<dt class="dlterm">Foreign key</dt>
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<dd>A field or set of fields in which each non-null value must match a value
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in the parent key of the related parent file. <p>The attributes (data type,
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length, and so forth) must be the same as the parent key of the parent file.</p>
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</dd>
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<dt class="dlterm">Parent file</dt>
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<dd>The file in a referential constraint relationship that contains the parent
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key.</dd>
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<dt class="dlterm">Dependent file</dt>
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<dd>The file in a referential constraint relationship that contains the foreign
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key. The dependent file is dependent on the parent file. That is, for every
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non-null value in the foreign key of the dependent file, there must be a corresponding
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non-null value in the parent key of the parent file.</dd>
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<dt class="dlterm">Check pending</dt>
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<dd>The state that occurs when the database does not know with certainty whether
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for a referential constraint this is true: for every non-null
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value in the foreign key of the dependent file, there must be a corresponding
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non-null value in the parent key of the parent file.</dd>
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<dt class="dlterm">Delete rule</dt>
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<dd>A definition of what action the database should take when there is an
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attempt to delete a parent record.</dd>
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<dt class="dlterm">Update rule</dt>
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<dd>A definition of what action the database should take when there is an
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attempt to update a parent record.</dd>
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</dl>
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</div>
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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="rbaforzahfrca.htm" title="These topics discuss how to use referential constraints in your database to ensure that it contains only valid data.">Ensure data integrity with referential constraints</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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