Sun Master Index provides a method by which you can create custom processing logic for the master index application. To do this, you need to define and name a custom plug-in, which is a Java class that performs the required functions. Once you create a custom plug-in, you incorporate it into the index by adding it to the appropriate configuration file. You can create custom update procedures and field validations, as well as define custom master index components. Update procedures must be referenced in the update policies of the Best Record file; field validations must be referenced in the Field Validation file; and custom components must be referenced in the configuration file for that component. For example, if you create a custom Query Builder, it must be listed in the Candidate Select file to be accessible to the master index application.