I am looking at an example WSDL

 <definitions xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd"
 xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
 xmlns:tns="http://mypackage/"
 xmlns:xsd="http://www.w3.org/2001/XMLSchema"
 xmlns="http://schemas.xmlsoap.org/wsdl/"
 targetNamespace="http://mypackage/" name="HelloService">
   <types>
     <xsd:schema>
       <xsd:import namespace="http://mypackage/"
       schemaLocation="http://localhost:8081/HelloWebService/HelloService?xsd=1">
       </xsd:import>
     </xsd:schema>
   </types>
   <message name="sayHello">
     <part name="parameters" element="tns:sayHello"></part>
   </message>
   <message name="sayHelloResponse">
     <part name="parameters" element="tns:sayHelloResponse"></part>
   </message>
   <portType name="Hello">
     <operation name="sayHello">
       <input message="tns:sayHello"></input>
       <output message="tns:sayHelloResponse"></output>
     </operation>
   </portType>
   <binding name="HelloPortBinding" type="tns:Hello">
     <soap:binding transport="http://schemas.xmlsoap.org/soap/http"
     style="document"></soap:binding>
     <operation name="sayHello">
       <soap:operation soapAction=""></soap:operation>
       <input>
         <soap:body use="literal"></soap:body>
       </input>
       <output>
         <soap:body use="literal"></soap:body>
       </output>
     </operation>
   </binding>
   <service name="HelloService">
     <port name="HelloPort" binding="tns:HelloPortBinding">
       <soap:address location="http://localhost:8081/HelloWebService/HelloService">
       </soap:address>
     </port>
</service>

and the referenced xsd is

 <?xml version="1.0" encoding="utf-8"?>
 <xs:schema xmlns:tns="http://mypackage/"
 xmlns:xs="http://www.w3.org/2001/XMLSchema" version="1.0"
 targetNamespace="http://mypackage/">
   <xs:element name="sayHello" type="tns:sayHello"></xs:element>
   <xs:element name="sayHelloResponse" type="tns:sayHelloResponse">
   </xs:element>
   <xs:complexType name="sayHello">
     <xs:sequence>
       <xs:element name="arg0" type="xs:string" minOccurs="0">
       </xs:element>
     </xs:sequence>
   </xs:complexType>
   <xs:complexType name="sayHelloResponse">
     <xs:sequence>
       <xs:element name="return" type="xs:string" minOccurs="0">
       </xs:element>
     </xs:sequence>
   </xs:complexType>
 </xs:schema>

When I use SoapUI to generate a request message, it looks like this

 <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:myp="http://mypackage/">
    <soapenv:Header/>
    <soapenv:Body>
       <myp:sayHello>
          <arg0>?</arg0>
       </myp:sayHello>
    </soapenv:Body>
 </soapenv:Envelope>

My question is, why doesn't arg0 need a namespace like ??

I am just using this as an example as the element that are children of soapenv always have a namespace prefix, however, the children of these children do not have any prefix. This is the case with soapUI and message sent by Axis2 generated stubs.

My questions are: 1. Why aren't there any namespace for arg0? 2. Is there a way to enforce myp prefix on arg0 from WSDL? If so, how? If not, why can't it be done?