A logger in the logback.xml acts as a pointer for the logs produced by the application:

    <logger name="puppetlabs.pcp" level="info" additivity="false">
      <appender-ref ref="PCP"/>
    </logger>

This example connects to the puppetlabs.pcp log in the Puppetserver application, and collects the info-level logs. The additivity=false flag tells the log to replace the file, rather than append to it. Finally, the appender-ref tag tells the logger which appender to use for the logging configuration.