# Prerequisites

The following software must be installed separately, it is not included with the Saxon download.

- To run Saxon you need at least a Java VM, and preferably a Java development environment. Saxon 8.3 will run with either JDK 1.4 (properly the Java 2 platform, Standard Edition, v 1.4) or JDK 1.5 (properly Java 2 Platform, Standard Edition 5.0).

- Saxon will no longer work with the Microsoft Java VM.

- Saxon implements APIs defined in JAXP 1.3 (JAXP is the Java API for XML Processing). JAXP 1.3 is a standard component in JDK 1.5, but if you are using JDK 1.4, it must be installed separately. For licensing reasons the JAXP package is not included in the Saxon distribution; instead you must download it separately from https://jaxp.dev.java.net/. This download includes two JAR files, `jaxp-api.jar` and `dom.jar`, which must be present on the classpath when running Saxon. Note that this means you cannot invoke Saxon using the `-jar` option, since this requires all files to be present in a single JAR archive, and ignores the CLASSPATH setting.

  Most XSLT and XQuery functionality in Saxon will work without installing JAXP 1.3. You need to install it if you are using DOM interfaces; if you are using the XPath API; or if you are using the schema validation API (applies to Saxon-SA only).

  It is likely that at some time in the future, Saxon will require J2SE 5.0

- Saxon has an option to work with a source tree constructed using JDOM. Saxon 8.3 is validated with JDOM 1.0; it probably also works with other recent releases. To use Saxon with JDOM, you need to add `saxon8-jdom.jar` to your CLASSPATH.

- Saxon now also has an option to work with a source tree constructed using XOM. Saxon 8.3 is tested with XOM 1.0b7. To use Saxon with XOM, you need to add `saxon8-xom.jar` to your CLASSPATH.

Saxon has been tested successfully in the past with a wide variety of XML parsers including Xerces, Lark, SUN Project X, Crimson, Piccolo, Oracle XML, xerces, xml4j, and xp. Use of a SAX2-compliant parser is now mandatory. All the relevant classes must be installed on your Java CLASSPATH.

Earlier releases of Saxon included a version of the Ælfred XML parser. This is no longer bundled with the Saxon distribution, because JDK 1.4 now includes an XML parser as standard, but the Ælfred XML parser remains available as a separate download from the Saxon site at SourceForge.

Saxon's DOM interface has been tested with the Crimson parser included as standard in Sun's JDK 1.4 platform and with the Xerces 2.5.0 DOM implementation.

Because Saxon is run from the command line, you might find it useful (under Microsoft Windows) to have a text editor with better command-line support than the standard DOS window. I use jEdit, which is an open source product with a wide-selection of optional plug-ins, including one for editing XQuery.

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