Serge NOEL
80 lines
3.7 KiB
Plaintext
80 lines
3.7 KiB
Plaintext
<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta name="generator" content="HTML Tidy for HTML5 for Apple macOS version 5.8.0">
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<title>JMRI: XML DTD Usage</title>
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<meta name="author" content="Bob Jacobsen">
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<meta name="keywords" content="JMRI technical code xml usage">
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</head>
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<body>
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<div id="mBody">
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<div id="mainContent">
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<h1>JMRI: XML DTD Usage</h1>
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<p class="important">This page describes the former usage of XML DTDs in JMRI before version
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2.9.4. The use of these DTDs in JMRI was replaced with <a href="XmlSchema.shtml">XML
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schema</a> in JMRI 2.9.4.</p>
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<p>In the JMRI distributions, the DTDs are stored in the <a href="/xml/DTD">xml/DTD</a>
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directory. Note that they are not stored in each directory alongside the XML files. There are
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just too many locations to keep such a set of DTD files up to date. JMRI itself, via the
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jmri.jmrit.XmlFile class, provides support for locating those files when the XML parser needs
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them.</p>
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Each file contains a DOCTYPE line that specifies a DTD name. There are three different
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methods used to locate the actual DTD file:
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<ul>
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<li>Web browsers look exactly where the DOCTYPE line specifies, and must find the DTD there
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to function.</li>
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<li>JMRI 1.8 and earlier assumes that the name is relative to the program's xml/DTD
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directory, and looks for it using that. In practice, this allows two forms for the DOCTYPE
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line:
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<ul>
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<li>name.dtd</li>
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<li>../DTD/name.dtd</li>
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</ul>
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Early XML files used both; the program itself could generate either depending on the
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circumstances.
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</li>
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<li>JMRI 1.9.2 and later provide a more powerful DTD search procedure using the <a href=
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"https://jmri.org/JavaDoc/doc/jmri/util/JmriLocalEntityResolver.html">jmri.util.JmriLocalEntityResolver</a>
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class. It parses the reference in the DOCTYPE and handles it in several ways:
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<ul>
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<li>If it's an HTTP URL, JMRI first attempts to find the corresponding file in the
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local distribution. If so, it uses the local copy, otherwise it attempts to load a copy
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from the Internet using the URL.</li>
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<li>If it's a file path that starts with "../DTD/", JMRI looks in it's local xml/DTD
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directory for the DTD file.</li>
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<li>If the path is just a filename, JMRI looks in it's local xml/DTD directory for the
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DTD file.</li>
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<li>In any other case, e.g. a local or absolute pathname, JMRI looks there for the DTD
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file. Relative pathnames are interpreted as starting from the JMRI install
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directory.</li>
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</ul>
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If the file can't be found, the XML file isn't opened. These JMRI versions write just the
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DTD filename in the DOCTYPE line when writing XML files. This provides complete backward
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compatibility with existing files and older versions of JMRI back to 1.7.1. At the same
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time, since it can handle HTTP URLs even without an Internet connection, it allows us to
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eventually move forward.
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</li>
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</ul>
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<strong>Starting with JMRI 2.9.4, JMRI uses <a href="XmlSchema.shtml">XML schema</a> instead
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of DTDs, and this process is different.</strong> <!--#include virtual="/help/en/parts/Footer.shtml" -->
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</div>
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</div>
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<script src="/js/help.js"></script>
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</body>
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</html>
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