95 lines
6.4 KiB
HTML
95 lines
6.4 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 name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Extended attributes" />
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<meta name="abstract" content="An extended attribute is information associated with an object that provides additional details about the object. The extended attribute consists of a name, which is used to refer to it, and a value. The value can be text, binary data, or another type of data." />
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<meta name="description" content="An extended attribute is information associated with an object that provides additional details about the object. The extended attribute consists of a name, which is used to refer to it, and a value. The value can be text, binary data, or another type of data." />
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<meta name="DC.subject" content="extended attributes, what are they?, naming guidelines" />
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<meta name="keywords" content="extended attributes, what are they?, naming guidelines" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxbasics.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1999, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1999, 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>Extended attributes</title>
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</head>
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<body id="rzaaxea"><a name="rzaaxea"><!-- --></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">Extended attributes</h1>
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<div><p>An extended attribute is information associated with an object
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that provides additional details about the object. The extended attribute
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consists of a name, which is used to refer to it, and a value. The value
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can be text, binary data, or another type of data.</p>
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<p>The extended attributes for an object exist only as long as the object
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exists.</p>
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<p>Extended attributes come in many varieties and can be used to contain a
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variety of information. You may need to be aware of the following three extended
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attributes, in particular: </p>
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<dl><dt class="dlterm">.SUBJECT</dt>
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<dd>A brief description of the content or purpose of the object.</dd>
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<dt class="dlterm">.TYPE</dt>
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<dd>The type of data in the object. The type of data might be text, binary,
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source for a program, a compiled program, or other information.</dd>
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<dt class="dlterm">.CODEPAGE</dt>
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<dd>The code page to be used for the object. The code page used for the object
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is also used for the extended attribute associated with the object.</dd>
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</dl>
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<p>A period (.) as the first character of the name means that the extended
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attribute is a standard system extended attribute (SEA), which is reserved
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for system use.</p>
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<p>Various objects in the various file systems may or may not have extended
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attributes. The QSYS.LIB and independent ASP QSYS.LIB file systems support
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three predefined extended attributes: .SUBJECT, .TYPE, and .CODEPAGE. In
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the document library services (QDLS) file system, folders and documents can
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have any kind of extended attribute. Some folders and documents may have
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extended attributes, and some may not. In the <span class="q">"root"</span> (/), QOpenSys,
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and user-defined file systems, all directories, stream files, and symbolic
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links can have extended attributes of any kind. Some, however, may not have
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any extended attributes at all.</p>
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<p><img src="./delta.gif" alt="Start of change" />The <span class="cmdname">Work with Object Links (WRKLNK)</span> command
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and <span class="cmdname">Display Object Links (DSPLNK)</span> command can be used to
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display the .SUBJECT extended attribute for an object. There is no other integrated
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file system support through which applications or users can access and change
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extended attributes. The only exceptions to this rule are the <span class="cmdname">Display
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a UDFS (DSPUDFS)</span> and the <span class="cmdname">Display Mounted File System Information
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(DSPMFSINF)</span> CL commands, which present extended attributes to users.<img src="./deltaend.gif" alt="End of change" /></p>
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<p>Extended attributes associated with some objects in the QDLS can, however,
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be changed through interfaces provided by the hierarchical file system (HFS).
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</p>
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<p>If a client PC is connected to an iSeries™ server through OS/2<sup>®</sup> or Windows<sup>®</sup>,
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the programming interfaces of the respective operating system (such as DosQueryFileInfo
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and DosSetFileInfo) can be used to query and set the extended attributes of
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any file object. OS/2 users can also change the extended attributes of
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an object on the desktop by using the settings notebook; that is, by selecting <samp class="codeph">Settings</samp> on
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the pop-up menu associated with the object.</p>
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<p>If you define extended attributes, use the following naming guidelines: </p>
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<ul><li>The name of an extended attribute can be up to 255 characters long.</li>
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<li>Do not use a period (.) as the first character of the name. An extended
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attribute whose name begins with a period is interpreted as a standard system
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extended attribute.</li>
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<li>To minimize the possibility of name conflicts, use a consistent naming
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structure for extended attributes. The following form is recommended: <pre> CompanyNameProductName.Attribute_Name</pre>
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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 class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaaxbasics.htm" title="This topic introduces the basic concepts of integrated file system, such as directory, link, path name, stream file, name continuity, extended attributes, and scanning support.">Integrated file system concepts</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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