This article is part of the Advanced User's Guide. It clarifies how to deal with external DTD declarations when parsing XML data.
XML documents often rely on Document Type Definitions (DTDs). While parsing a document with BaseX, entities can be resolved with respect to that particular DTD. By default, the DTD is only used for entity resolution.
XHTML, for example, defines its doctype via the following line:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
xhtml1-strict.dtd obviously involves network traffic. When dealing with single files, this may seem tolerable, but
importing large collections benefits from caching these resources. Depending on the remote server, you will experience significant speed improvements when caching DTDs locally.
XML Entity and URI Resolvers
BaseX comes with a default URI resolver that is usable out of the box.
To enable entity resolving you have to provide a valid XML Catalog file, so that the parser knows where to look for mirrored DTDs.
A simple working example for XHTML might look like this:
<?xml version="1.0"?> <catalog prefer="system" xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog"> <rewriteSystem systemIdStartString="http://www.w3.org/TR/xhtml1/DTD/" rewritePrefix="file:///path/to/dtds/" /> </catalog>
This rewrites all systemIds starting with: http://www.w3.org/TR/xhtml1/DTD/ to file:///path/to/dtds/.
The XHTML DTD
xhtml1-strict.dtd and all its linked resources will now be loaded from the specified path.
When running BaseX in GUI mode, simply provide the path to your XML Catalog file in the Parsing Tab of the Database Creation Dialog.
Console & Server Mode
To enable Entity Resolving in Console Mode, assign a directory path to the
CATFILE option. All subsequent
ADD commands will use the specified catalog file to resolve entities.
The paths to your catalog file and the actual DTDs are either absolute or relative to the current working directory. When using BaseX in Client-Server-Mode, this is relative to the server's working directory.
Entity resolving only works if the internal XML parser is switched off (which is the default case). If you use the internal parser, you can manually specify whether you want to parse DTDs and entities or not.
Using other Resolvers
There might be some cases when you do not want to use the built-in resolver that Java provides by default
To use it add resolver.jar to the classpath when starting BaseX:
java -cp basex.jar:resolver.jar org.basex.BaseXServer