# XML data types and operators

Derby supports the XML data type and a set of operators that work with the XML data type, but does not provide JDBC support for the XML data type. The XML data type and operators are based on a small subset of the SQL/XML specification.

The XML data type and operators are defined only in the SQL layer.

There is no JDBC-side support for XML data types. It is not possible to bind directly into an XML value or to retrieve an XML value directly from a result set. Instead, you must bind and retrieve the XML data as Java strings or character streams by explicitly specifying the appropriate XML operator as part of the SQL statements:

- Use the XMLPARSE operator for binding data into XML values.
- Use the XMLSERIALIZE operator to retrieve XML values from a result set.

Additionally, there is no JDBC metadata support for the XML data type.

The XML data type is not allowed in any of the clauses or operations that are described in the section on expressions on LONG data types in Derby and standards.

For the XML operators to work properly, Derby requires that a JAXP parser, such as Apache Xerces, and Apache Xalan are included in the Java classpath. If either the parser or Xalan are missing from the classpath, Derby disallows any XML-related operations.

#### Classpath and version issues

Most Java Virtual Machines (JVMs) that are version 1.4 or later have a JAXP parser embedded in the JVM. If you are using one of these JVMs, you may not need to add any classes to your classpath. Some exceptions exist:

- In most version 1.4.2 JVMs, the version of Xalan that comes with the JVM is not new enough, so you must override the version of Xalan in the JVM with a newer version by using the Endorsed Standards Override Mechanism described at http://java.sun.com/j2se/1.4.2/docs/guide/standards/. To use this mechanism, download and install a binary distribution of Xalan from Apache and set the system property `java.endorsed.dirs` to point to the Xalan installation directory.
- After JVM version 1.4, Sun renamed the JAXP packages. Derby cannot find these renamed packages. If you are using a Sun JVM later than version 1.4, download and install a binary distribution of Xalan from Apache and place the `xalan.jar` file in your classpath. The `xalan.jar` file automatically puts into the classpath the other required jars that are in the same directory.

Parent topic: Derby and standards