Jasper Report

I create a jrxml file using ireport and try to use jasper reports and i have a question about the < Parameters > why we use the parameters ?

the execption is java.lang.reflect.InvocationTargetException org.bonitasoft.engine.bpm.connector.ConnectorExecutionException: USERNAME=install | org.bonitasoft.engine.core.connector.exception.SConnectorException: org.bonitasoft.engine.connector.exception.SConnectorException: java.util.concurrent.ExecutionException: org.bonitasoft.engine.connector.exception.SConnectorValidationException: org.bonitasoft.engine.connector.ConnectorValidationException: Error validating connector org.bonitasoft.connectors.jasper.CreateReportFromDataBase:

<property name="ireport.zoom" value="1.0"/>

<property name="ireport.x" value="0"/>

<property name="ireport.y" value="0"/>

<style name="Title" fontName="Arial" fontSize="26" isBold="true" pdfFontName="Helvetica-Bold"/>

<style name="SubTitle" forecolor="#666666" fontName="Arial" fontSize="18"/>

<style name="Column header" forecolor="#666666" fontName="Arial" fontSize="12" isBold="true"/>

<style name="Detail" fontName="Arial" fontSize="12"/>

<subDataset name="dataset1" uuid="b94aecc0-d13c-4a29-82cc-4f228b26fdec"/>

<queryString language="SQL">

    <![CDATA[select * from  userinfo]]>

</queryString>

<field name="id" class="java.lang.Integer"/>

<field name="processID" class="java.lang.String"/>

<field name="firstname" class="java.lang.String"/>

<field name="secondname" class="java.lang.String"/>

<field name="lastname" class="java.lang.String"/>