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7<title>XML file associations with DTDs and XML schemas</title>
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17<h1 class="topictitle1">XML file associations with DTDs and XML schemas</h1>
18<div><p>There are two different ways to associate XML files with DTDs or
19XML schemas.</p><ol><li>Direct association - The XML file contains either the name of a DTD in
20its doctype declaration (for example, &lt;!DOCTYPE root-element SYSTEM " <var class="varname">dtdfile.dtd</var>"
21&gt;, where <var class="varname">dtdfile.dtd</var> is the name of the DTD file) or it
22contains the path of an XML schema in the schemaLocation attribute of the
23XML file root element (for example, &lt;xsi:schemaLocation="http://www.ibm.com
24 <var class="varname">schema.xsd</var>"&gt;, where <var class="varname">schema.xsd</var> is
25the name of the XML schema.</li>
26<li>XML Catalog entry  - You can register DTD and XML schema files in
27the XML Catalog and associate them with a <var class="varname">Key</var> that represents
28them. You can then refer to a DTD or XML schema file <var class="varname">Key</var> from
29an XML file instead of referring directly to the DTD or XML schema file. An
30XML Catalog entry contains two parts - the Key (which represents the DTD or
31XML schema) and a URI (which contains information about the DTD or XML schema
32location).</li>
33</ol>
34<div class="skipspace"><h4 class="sectiontitle">How an association works </h4><b>Associating an XML
35file with a DTD </b><div class="p">If an XML file is associated with a DTD, a DOCTYPE
36tag such as the following is included in the XML file:<pre>&lt;!DOCTYPE root-name PUBLIC "<var class="varname">InvoiceId</var>" "<var class="varname">C:\mydtds\Invoice.dtd</var>"&gt;</pre>
37</div>
38<p><var class="varname">InvoiceId</var> is the public identifier of
39the DTD file. It is used to associate the XML file with a DTD file (in this
40case, the DTD file is <var class="varname">Invoice.dtd</var>). If the public identifier
41InvoiceId corresponds to the <var class="varname">Key</var> of the XML Catalog entry
42for Invoice.dtd, then the <var class="varname">URI</var> of the XML Catalog entry
43(which contains information about the location of Invoice.dtd) is used to
44locate the DTD. Otherwise, the DOCTYPE's system identifier ( <var class="varname">"C:\mydtds\Invoice.dtd"</var>),
45which refers directly to the file system location of the DTD, is used to locate
46the DTD. </p>
47<p> <b>Note</b>: You can also use a system identifier as
48a Key in an XML Catalog entry. If you use a system identifier as a Key, a
49DOCTYPE tag such as the following is included in an XML file:</p>
50<pre>&lt;!DOCTYPE Root-name SYSTEM "<var class="varname">MyDTD.dtd</var>"&gt; </pre>
51<p>where <var class="varname">MyDTD.dtd</var> is the system identifier that corresponds
52to the Key of an XML Catalog entry.</p>
53</div>
54<div class="skipspace"><b>Associating an XML file with an XML schema</b><p>If an XML file
55is associated with an XML schema, one or more schema location attributes are
56included in the XML file. The information in the schemaLocation is provided
57as a "hint" to the XML processor. Examples of schemaLocation attributes are
58shown below: </p>
59<div class="p"> <b>Example 1 </b><pre>&lt;purchaseOrder xmlns="http://www.ibm.com"
60xsi:schemaLocation="http://www.ibm.com C:\myschemas\PurchaseOrder.xsd"&gt;
61&lt;shipTo country="US"&gt; 
62...</pre>
63 </div>
64<div class="p"><b>Example 2 </b><pre>&lt;purchaseOrder xmlns="http://www.ibm.com"
65xsi:schemaLocation="http://www.ibm.com PO.xsd"&gt;
66&lt;shipTo country="US"&gt; 
67....</pre>
68 </div>
69<p>In Example 1, the schemaLocation 'hint' ('C:\myschemas\PurchaseOrder.xsd')
70refers directly to the file system location or URI of the XML schema. In this
71case, the schema file will be located by the XML processor directly.</p>
72<p>In
73Example 2, the schemaLocation 'hint' ('PO.xsd') refers to an XML Catalog entry.
74PO.xsd corresponds to the <var class="varname">Key</var> of the XML Catalog entry
75for PurchaseOrder.xsd, and the URI of the XML Catalog entry (which contains
76information about the location of PurchaseOrder.xsd) will be used to located
77the XML schema.</p>
78<p>In both examples, <samp class="codeph">http://www.ibm.com</samp> in
79the <samp class="codeph">xsi:schemaLocation</samp> tag is a URI that identifies the namespace
80for the XML schema. </p>
81<div class="p">You can also use a namespace as a Key for
82an XML Catalog entry. If you use a namespace as a Key, a schemaLocation tag
83such as the following is included in an XML file:<pre>&lt;purchaseOrder xmlns:="www.ibm.com" 
84 xsi:schemaLocation="http://www.ibm.com po/xsd/PurchaseOrder.xsd "&gt;</pre>
85</div>
86<p>The
87schemaLocation attribute points to both the Key and the actual location of
88the schema.</p>
89<p><b>DTD or XML schema resides on a remote server</b></p>
90<p>Several
91functions in the XML editor, such as validation and content assist, require
92the availability of a DTD or an XML schema. The product documentation provides
93usage information for cases when the DTD or XML schema resides on your local
94machine. However, in many cases, the DTD or XML schema may reside on a remote
95server, for example:</p>
96<p><samp class="codeph">&lt;!DOCTYPE Catalog PUBLIC "abc/Catalog"
97"http://xyz.abc.org/dtds/catalog.dtd"&gt;</samp></p>
98<p>Normally, this case
99poses no problem, because the DTD or XML schema can be retrieved from the
100remote server. However, if you are behind a firewall, and do not have a SOCKSified
101system, the workbench currently does not provide a way for you to specify
102a socks server for retrieving a DTD or XML schema. If you are unable to SOCKSify
103your system, the workaround for this problem is to retrieve a copy of the
104DTD or XML schema (using a Web browser, for example) and save that copy on
105your local machine. Then, you can either place a local copy in the same project
106as your XML file, or use the XML Catalog to associate a public identifier
107with the DTD's (local) location.</p>
108<p><b>Note</b>: If you have an XML file
109associated with an XML schema or DTD that is elsewhere in the network, and
110you are working on a machine disconnected from the network, you can follow
111the steps described above if you want to use content assist or validate your
112XML file. </p>
113</div>
114<div class="skipspace"><h4 class="sectiontitle">Advantages of XML Catalog entry associations</h4><p>If
115you create a direct association between an XML file and an XML schema or DTD
116file, any time you change the location of the schema or DTD you have to track
117down and update all of the referencing XML files with the new location of
118the DTD or schema. If, however, you associate an XML file with an XML schema
119or DTD Key, then, when you change the location of the schema or DTD, you only
120have to update the XML Catalog entry, instead of each individual XML file. </p>
121<p>For
122example, you have a DTD called "Building.dtd", which is associated with five
123XML files - Office.xml, House.xml, Apartment.xml, Bank.xml, and PostOffice.xml.
124You move the DTD file Building.dtd to a new location. If you have a direction
125association between Building.dtd and all the XML files, you will have to update
126the &lt;DOCTTYPE&gt; declaration in each XML file to reflect the new location
127of Building.dtd.  If, however, you have an XML Catalog association, and
128all the XML files just refer to the Key of Building.dtd, then you only have
129to update the URI and all the XML files will point to the new location of
130Building.dtd.</p>
131</div>
132<div class="skipspace"><h4 class="sectiontitle">Updating an entry in the XML Catalog</h4><p>After you have
133updated an entry in the XML Catalog, you may need to refresh the XML editor
134view so that it uses the new information. To do this, click the <span class="uicontrol">Reload
135Dependencies</span> toolbar button <img src="../images/rldgrmr.gif" /> and
136the view will be updated using the current XML Catalog settings. You only
137need to refresh the XML editor view when you have an XML file open that references
138the XML Catalog entry that was updated.</p>
139<p>For more information, refer
140to the related concepts and tasks below.</p>
141<p>(c) Copyright 2001, World Wide
142Web Consortium (Massachusetts Institute of Technology, Institut National de
143Recherche en Informatique et en Automatique, Keio University).</p>
144</div>
145</div>
146
147<div>
148<blockquote>
149<div class="ulchildlink"><b><a href="../topics/txmlcat.html">Adding an entry to the XML Catalog</a></b><br />
150</div>
151<div class="ulchildlink"><b><a href="../topics/tedtgram.html">Updating XML files with changes made to DTDs and schemas</a></b><br />
152If you make changes to a DTD file or XML schema associated with
153an XML file (that is currently open), click <span class="uicontrol">XML &gt; Reload Dependencies</span> to
154update the XML file with these changes.</div>
155</blockquote>
156<p><b class="relconceptshd">Related concepts</b><br />
157<a href="../topics/cwxmledt.html" title="The XML editor is a tool for creating and viewing XML files">XML editor</a><br />
158</p>
159<p><b class="reltaskshd">Related tasks</b><br />
160<a href="../topics/tedtcnst.html" title="In the Design view, when you edit an XML file that has a set of constraints (that is, a set of rules) defined by a DTD or an XML schema, you can turn the constraints on and off to provide flexibility in the way you edit, but still maintain the validity of the document periodically.">Editing with DTD or XML schema constraints</a><br />
161<a href="../topics/tedtdoc.html" title="The DOCTYPE declaration in an XML file is used at the beginning of it to associate it with a DTD file. You can edit your DOCTYPE declaration to change the DTD file your XML file is associated with.">Editing your DOCTYPE declaration</a><br />
162<a href="../topics/txmlcat.html" title="Adding an entry to the XML Catalog"></a><br />
163<a href="../topics/tedtgram.html" title="If you make changes to a DTD file or XML schema associated with an XML file (that is currently open), click XML &gt; Reload Dependencies to update the XML file with these changes.">Updating XML files with changes made to DTDs and schemas</a><br />
164<a href="../topics/tedtsch.html" title="Your namespace information is used to provide various information about the XML file, such as the XML schema it is associated with. ">Editing your namespace information</a><br />
165<a href="../topics/tedtproc.html" title="A processing instruction is a syntax in XML for passing instructions along to the application using an XML document.">Editing your XML processing instructions</a><br />
166<a href="../topics/txedtdes.html" title="The XML editor has a Design view, which represents the XML file simultaneously as a table and a tree. This helps make navigation and editing easier. Content and attribute values can be edited directly in the table cells, while pop-up menus on the tree elements give alternatives that are valid for that particular element.">Editing in the Design view</a><br />
167<a href="../topics/txedtsrc.html" title="You can use the Source view to view and work with a file's source code directly.">Editing in the Source view</a><br />
168</p>
169</div><p>
170 (C) Copyright IBM Corporation 2000, 2005. All Rights Reserved.
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