# Extending an XML catalog file

You can update either the main DITA-OT XML catalog or the XML catalog that is used by the PDF plug-in. This enables DITA-OT to support new specializations and document-type shells.

## About this task

You can use the dita.specialization.catalog.relative and org.dita.pdf2.catalog.relative extension points to update the DITA-OT catalog files.

Remember:
The dita.specialization.catalog extension is deprecated. Use dita.specialization.catalog.relative instead.

## Procedure

1. Using the OASIS catalog format, create an XML catalog file that contains only the new values that you want to add to a DITA-OT catalog file.
2. Create a plugin.xml file that contains the following content:

       <plugin id="plugin-id">
         <feature extension="extension-point" file="file"/>
       </plugin>

   where:
   - plugin-id is the plug-in identifier, for example, `com.example.catalog`.
   - extension-point is either dita.specialization.catalog.relative or org.dita.pdf2.catalog.relative.
   - file is the name of the new catalog file, for example, catalog-dita.xml.
3. Save the new XML catalog file to your plug-in. Be sure that the local file references are relative to the location of the catalog and plug-in.
4. Use the dita install subcommand to install the plug-in.
   Note:
   For more information, see Installing plug-ins.

## Results

The catalog entries inside of the new catalog file are added to the core DITA-OT catalog file.

## Example

This example assumes that catalog-dita.xml contains an OASIS catalog for any document-type shells inside this plug-in. The catalog entries in catalog-dita.xml are relative to the catalog itself; when the plug-in is installed, they are added to the core DITA-OT catalog (with the correct path).

    <plugin id="com.example.catalog">
      <feature extension="dita.specialization.catalog.relative"
               file="catalog-dita.xml"/>
    </plugin>