| <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/1999/REC-html401-19991224/loose.dtd"> |
| <html> |
| <head> |
| <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> |
| <link rel="SHORTCUT ICON" href="/favicon.ico"> |
| <style type="text/css"><!-- |
| TD {font-family: Verdana,Arial,Helvetica} |
| BODY {font-family: Verdana,Arial,Helvetica; margin-top: 2em; margin-left: 0em; margin-right: 0em} |
| H1 {font-family: Verdana,Arial,Helvetica} |
| H2 {font-family: Verdana,Arial,Helvetica} |
| H3 {font-family: Verdana,Arial,Helvetica} |
| A:link, A:visited, A:active { text-decoration: underline } |
| --></style> |
| <title>Entities or no entities</title> |
| </head> |
| <body bgcolor="#8b7765" text="#000000" link="#000000" vlink="#000000"> |
| <table border="0" width="100%" cellpadding="5" cellspacing="0" align="center"><tr> |
| <td width="180"> |
| <a href="http://www.gnome.org/"><img src="gnome2.png" alt="Gnome2 Logo"></a><a href="http://www.w3.org/Status"><img src="w3c.png" alt="W3C Logo"></a><a href="http://www.redhat.com/"><img src="redhat.gif" alt="Red Hat Logo"></a><div align="left"><a href="http://xmlsoft.org/"><img src="Libxml2-Logo-180x168.gif" alt="Made with Libxml2 Logo"></a></div> |
| </td> |
| <td><table border="0" width="90%" cellpadding="2" cellspacing="0" align="center" bgcolor="#000000"><tr><td><table width="100%" border="0" cellspacing="1" cellpadding="3" bgcolor="#fffacd"><tr><td align="center"> |
| <h1>The XML C library for Gnome</h1> |
| <h2>Entities or no entities</h2> |
| </td></tr></table></td></tr></table></td> |
| </tr></table> |
| <table border="0" cellpadding="4" cellspacing="0" width="100%" align="center"><tr><td bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr> |
| <td valign="top" width="200" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td> |
| <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Main Menu</b></center></td></tr> |
| <tr><td bgcolor="#fffacd"> |
| <form action="search.php" enctype="application/x-www-form-urlencoded" method="GET"> |
| <input name="query" type="TEXT" size="20" value=""><input name="submit" type="submit" value="Search ..."> |
| </form> |
| <ul> |
| <li><a href="index.html">Home</a></li> |
| <li><a href="intro.html">Introduction</a></li> |
| <li><a href="FAQ.html">FAQ</a></li> |
| <li><a href="docs.html">Documentation</a></li> |
| <li><a href="bugs.html">Reporting bugs and getting help</a></li> |
| <li><a href="help.html">How to help</a></li> |
| <li><a href="downloads.html">Downloads</a></li> |
| <li><a href="news.html">News</a></li> |
| <li><a href="XMLinfo.html">XML</a></li> |
| <li><a href="XSLT.html">XSLT</a></li> |
| <li><a href="python.html">Python and bindings</a></li> |
| <li><a href="architecture.html">libxml architecture</a></li> |
| <li><a href="tree.html">The tree output</a></li> |
| <li><a href="interface.html">The SAX interface</a></li> |
| <li><a href="xmldtd.html">Validation & DTDs</a></li> |
| <li><a href="xmlmem.html">Memory Management</a></li> |
| <li><a href="encoding.html">Encodings support</a></li> |
| <li><a href="xmlio.html">I/O Interfaces</a></li> |
| <li><a href="catalog.html">Catalog support</a></li> |
| <li><a href="library.html">The parser interfaces</a></li> |
| <li><a href="entities.html">Entities or no entities</a></li> |
| <li><a href="namespaces.html">Namespaces</a></li> |
| <li><a href="upgrade.html">Upgrading 1.x code</a></li> |
| <li><a href="threads.html">Thread safety</a></li> |
| <li><a href="DOM.html">DOM Principles</a></li> |
| <li><a href="example.html">A real example</a></li> |
| <li><a href="contribs.html">Contributions</a></li> |
| <li><a href="xmlreader.html">The Reader Interface</a></li> |
| <li><a href="tutorial/index.html">Tutorial</a></li> |
| <li><a href="guidelines.html">XML Guidelines</a></li> |
| <li> |
| <a href="xml.html">flat page</a>, <a href="site.xsl">stylesheet</a> |
| </li> |
| </ul> |
| </td></tr> |
| </table> |
| <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>Related links</b></center></td></tr> |
| <tr><td bgcolor="#fffacd"><ul> |
| <li><a href="http://mail.gnome.org/archives/xml/">Mail archive</a></li> |
| <li><a href="http://xmlsoft.org/XSLT/">XSLT libxslt</a></li> |
| <li><a href="http://phd.cs.unibo.it/gdome2/">DOM gdome2</a></li> |
| <li><a href="http://www.aleksey.com/xmlsec/">XML-DSig xmlsec</a></li> |
| <li><a href="ftp://xmlsoft.org/">FTP</a></li> |
| <li><a href="http://www.zlatkovic.com/projects/libxml/">Windows binaries</a></li> |
| <li><a href="http://garypennington.net/libxml2/">Solaris binaries</a></li> |
| <li><a href="http://www.zveno.com/open_source/libxml2xslt.html">MacOsX binaries</a></li> |
| <li><a href="http://sourceforge.net/projects/libxml2-pas/">Pascal bindings</a></li> |
| <li><a href="http://bugzilla.gnome.org/buglist.cgi?product=libxml&product=libxml2">Bug Tracker</a></li> |
| </ul></td></tr> |
| </table> |
| <table width="100%" border="0" cellspacing="1" cellpadding="3"> |
| <tr><td colspan="1" bgcolor="#eecfa1" align="center"><center><b>API Indexes</b></center></td></tr> |
| <tr><td bgcolor="#fffacd"><ul> |
| <li><a href="APIchunk0.html">Alphabetic</a></li> |
| <li><a href="APIconstructors.html">Constructors</a></li> |
| <li><a href="APIfunctions.html">Functions/Types</a></li> |
| <li><a href="APIfiles.html">Modules</a></li> |
| <li><a href="APIsymbols.html">Symbols</a></li> |
| </ul></td></tr> |
| </table> |
| </td></tr></table></td> |
| <td valign="top" bgcolor="#8b7765"><table border="0" cellspacing="0" cellpadding="1" width="100%"><tr><td><table border="0" cellspacing="0" cellpadding="1" width="100%" bgcolor="#000000"><tr><td><table border="0" cellpadding="3" cellspacing="1" width="100%"><tr><td bgcolor="#fffacd"> |
| <p>Entities in principle are similar to simple C macros. An entity defines an |
| abbreviation for a given string that you can reuse many times throughout the |
| content of your document. Entities are especially useful when a given string |
| may occur frequently within a document, or to confine the change needed to a |
| document to a restricted area in the internal subset of the document (at the |
| beginning). Example:</p> |
| <pre>1 <?xml version="1.0"?> |
| 2 <!DOCTYPE EXAMPLE SYSTEM "example.dtd" [ |
| 3 <!ENTITY xml "Extensible Markup Language"> |
| 4 ]> |
| 5 <EXAMPLE> |
| 6 &xml; |
| 7 </EXAMPLE></pre> |
| <p>Line 3 declares the xml entity. Line 6 uses the xml entity, by prefixing |
| its name with '&' and following it by ';' without any spaces added. There |
| are 5 predefined entities in libxml allowing you to escape characters with |
| predefined meaning in some parts of the xml document content: |
| <strong>&lt;</strong> for the character '<', <strong>&gt;</strong> |
| for the character '>', <strong>&apos;</strong> for the character ''', |
| <strong>&quot;</strong> for the character '"', and |
| <strong>&amp;</strong> for the character '&'.</p> |
| <p>One of the problems related to entities is that you may want the parser to |
| substitute an entity's content so that you can see the replacement text in |
| your application. Or you may prefer to keep entity references as such in the |
| content to be able to save the document back without losing this usually |
| precious information (if the user went through the pain of explicitly |
| defining entities, he may have a a rather negative attitude if you blindly |
| substitute them as saving time). The <a href="html/libxml-parser.html#XMLSUBSTITUTEENTITIESDEFAULT">xmlSubstituteEntitiesDefault()</a> |
| function allows you to check and change the behaviour, which is to not |
| substitute entities by default.</p> |
| <p>Here is the DOM tree built by libxml for the previous document in the |
| default case:</p> |
| <pre>/gnome/src/gnome-xml -> ./xmllint --debug test/ent1 |
| DOCUMENT |
| version=1.0 |
| ELEMENT EXAMPLE |
| TEXT |
| content= |
| ENTITY_REF |
| INTERNAL_GENERAL_ENTITY xml |
| content=Extensible Markup Language |
| TEXT |
| content=</pre> |
| <p>And here is the result when substituting entities:</p> |
| <pre>/gnome/src/gnome-xml -> ./tester --debug --noent test/ent1 |
| DOCUMENT |
| version=1.0 |
| ELEMENT EXAMPLE |
| TEXT |
| content= Extensible Markup Language</pre> |
| <p>So, entities or no entities? Basically, it depends on your use case. I |
| suggest that you keep the non-substituting default behaviour and avoid using |
| entities in your XML document or data if you are not willing to handle the |
| entity references elements in the DOM tree.</p> |
| <p>Note that at save time libxml enforces the conversion of the predefined |
| entities where necessary to prevent well-formedness problems, and will also |
| transparently replace those with chars (i.e. it will not generate entity |
| reference elements in the DOM tree or call the reference() SAX callback when |
| finding them in the input).</p> |
| <p> |
| <span style="background-color: #FF0000">WARNING</span>: handling entities |
| on top of the libxml SAX interface is difficult!!! If you plan to use |
| non-predefined entities in your documents, then the learning curve to handle |
| then using the SAX API may be long. If you plan to use complex documents, I |
| strongly suggest you consider using the DOM interface instead and let libxml |
| deal with the complexity rather than trying to do it yourself.</p> |
| <p><a href="bugs.html">Daniel Veillard</a></p> |
| </td></tr></table></td></tr></table></td></tr></table></td> |
| </tr></table></td></tr></table> |
| </body> |
| </html> |