What does "The prefix "vm" for element "vm:endpoint" is not bound." means and how to solve it?

Question

I am trying to integrate mule with drools, I have mainly followed the tutorial here but I am getting this error :

"The prefix "vm" for element "vm:endpoint" is not bound."

can anyone help me solve this problem?

following is my .drl file and mule flow files.

<?xml version="1.0" encoding="UTF-8"?>
<mule 
xmlns:bpm="http://www.mulesoft.org/schema/mule/bpm"
xmlns:http="http://www.mulesoft.org/schema/mule/http"
xmlns:tracking="http://www.mulesoft.org/schema/mule/ee/tracking" xmlns="http://www.mulesoft.org/schema/mule/core"
xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
xmlns:spring="http://www.springframework.org/schema/beans" version="EE-3.6.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation=
"http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
http://www.mulesoft.org/schema/mule/ee/tracking http://www.mulesoft.org/schema/mule/ee/tracking/current/mule-tracking-ee.xsd
http://www.mulesoft.org/schema/mule/bpm http://www.mulesoft.org/schema/mule/bpm/3.6/mule-bpm.xsd">
    <http:listener-config name="HTTP_Listener_Configuration"
    host="localhost" port="8084" doc:name="HTTP Listener Configuration" />

    <spring:beans>
        <spring:bean id="dto" class="com.hamgam.hit.esb.XMLDTO" scope="singleton" />
        <spring:bean id="dto-convertor" class="com.hamgam.hit.esb.XMLToDTO" scope="singleton" />
        <spring:bean id="rule-convertor" class="com.hamgam.hit.esb.RuleXMLToDRL" scope="singleton" />           
    </spring:beans>

    <bpm:drools />

    <flow name="basic_tutorialFlow">
        <http:listener config-ref="HTTP_Listener_Configuration" path="/{name}" doc:name="HTTP" />
        <vm:endpoint name = "emc" path="drool.msg" />
        <set-variable  variableName="name" value="#[message.inboundProperties['http.uri.params']['name']]" />       
        <set-variable variableName="msg" value="#[payload]"/>
        <logger level="DEBUG" doc:name="Logger" message="Current path is flowVars['name']" />

        <expression-component>
        app.registry['dto'] = app.registry['dto-convertor'].convert(flowVars['name']);
        </expression-component> 

        <bpm:rules rulesDefinition="rule.drl" cepMode="true" initialFacts-ref="dto" entryPoint="XMLDTO stream" />
    
        <choice doc:name="Choice">
            <when expression="#[flowVars.emc == 'KeyValueMatched']">
            <set-payload doc:name="Set Payload" value="#['KeyValueMatched! You are with us on 8084. ' + flowVars['name'] + '. Today is ' + server.dateTime.format('dd/MM/yy') + '.' ]" />
            </when>
            <otherwise>
            <set-payload doc:name="Set Payload" value="#['Nothing! You are with us on 8084. ' + flowVars['name'] + '. Today is ' + server.dateTime.format('dd/MM/yy') + '.' ]" />
            </otherwise>
        </choice>

    </flow>
</mule>

and the drl file :

global org.mule.module.bpm.MessageService mule;    
import com.me.mit.esb.*;
 
rule "La Vita Ebela"    
dialect "mvel"

when
    $x:XMLDTO( inputXML == "inputXML" )
then
    mule.generateMessage("emc",  "KeyValueMatched", null, MessageExchangePattern.ONE_WAY);
end

Answer 1

You have to add XML namespache and scema reference to your xml file:

XML namespace:
   xmlns:vm="http://www.mulesoft.org/schema/mule/vm" 

XML Schema Location:
http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/3.6/mule-vm.xsd 

So it looks like so:

<mule 
    xmlns:bpm="http://www.mulesoft.org/schema/mule/bpm"
    xmlns:vm="http://www.mulesoft.org/schema/mule/vm" 

    xmlns:http="http://www.mulesoft.org/schema/mule/http"
    xmlns:tracking="http://www.mulesoft.org/schema/mule/ee/tracking" xmlns="http://www.mulesoft.org/schema/mule/core"
    xmlns:doc="http://www.mulesoft.org/schema/mule/documentation"
    xmlns:spring="http://www.springframework.org/schema/beans" version="EE-3.6.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation=
    "http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-current.xsd
    http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd
    http://www.mulesoft.org/schema/mule/http http://www.mulesoft.org/schema/mule/http/current/mule-http.xsd
    http://www.mulesoft.org/schema/mule/ee/tracking http://www.mulesoft.org/schema/mule/ee/tracking/current/mule-tracking-ee.xsd
    http://www.mulesoft.org/schema/mule/bpm http://www.mulesoft.org/schema/mule/bpm/3.6/mule-bpm.xsd
    http://www.mulesoft.org/schema/mule/vm http://www.mulesoft.org/schema/mule/vm/3.6/mule-vm.xsd 
">