This is actually a confirmation to SFDC (so if some God in the SFDC heaven or any other wild heaven is watching me, please answer to my question...)

I got an parse error when I tried to generate apex class from WSDL by WSDL2APEX.

Error: Unable to find schema for element; {http://www.w3.org/2001/XMLSchema}string

like this post: http://community.salesforce.com/sforce/board/message?board.id=general_development&message.id=28929

Long story in short, I found the reason. Request/Response message doesn't accept just a xsd:string. It has to be complexType.

This post

http://community.salesforce.com/sforce/board/message?board.id=apex&message.id=2058

mentioned that SFDC doesn't support simpleType restriction, but I wonder it also mens it doesn't support single-standard type Request/Response.

Question: Am I correct? which means there is no way to use this WSDL? (this WSDL is from a product, so I can't change the actual format... only way to use this is to create a custom HTTP request...)

So, this doesn't work, because SessionID is xsd:string.

<definitions xmlns:tns="http://www.hoge.com/hoge/Object"
             xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
             xmlns="http://schemas.xmlsoap.org/wsdl/"
             xmlns:xsd="http://www.w3.org/2001/XMLSchema"
             name="Companies"
             targetNamespace="http://www.hoge.com/hoge/Object">
   <types>
      <xsd:schema elementFormDefault="qualified" targetNamespace="http://www.hoge.com/hoge/Object">
         <xsd:element name="Login">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element minOccurs="1" name="Username" type="xsd:string"/>
                  <xsd:element minOccurs="0" name="Password" type="xsd:string"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="SessionID" type="xsd:string"/>
      </xsd:schema>
   </types>
   <message name="Login">
      <part element="tns:Login" name="parameters"/>
   </message>
   <message name="LoginResponse">
      <part element="tns:SessionID" name="body"/>
   </message>
   <portType name="CompaniesPort">
      <operation name="Login">
         <input message="tns:Login"/>
         <output message="tns:LoginResponse"/>
      </operation>
   </portType>
   <binding name="CompaniesSoapBinding" type="tns:CompaniesPort">
      <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/>
      <operation name="Login">
         <soap:operation soapAction="https://morethan/foo/bar/Login" style="document"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
   </binding>
   <service name="CompaniesService">
      <port binding="tns:CompaniesSoapBinding" name="CompaniesService">
         <soap:address location="https://morethan/foo/bar"/>
      </port>
   </service>
</definitions>

 This works because LoginOut is complexType.

<definitions xmlns:tns="http://www.hoge.com/hoge/Object"
             xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
             xmlns="http://schemas.xmlsoap.org/wsdl/"
             xmlns:xsd="http://www.w3.org/2001/XMLSchema"
             name="Companies"
             targetNamespace="http://www.hoge.com/hoge/Object">
   <types>
      <xsd:schema elementFormDefault="qualified" targetNamespace="http://www.hoge.com/hoge/Object">
         <xsd:element name="Login">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element minOccurs="1" name="Username" type="xsd:string"/>
                  <xsd:element minOccurs="0" name="Password" type="xsd:string"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
         <xsd:element name="LoginOut">
            <xsd:complexType>
               <xsd:sequence>
                  <xsd:element name="SessionID" type="xsd:string"/>
               </xsd:sequence>
            </xsd:complexType>
         </xsd:element>
      </xsd:schema>
   </types>
   <message name="Login">
      <part element="tns:Login" name="parameters"/>
   </message>
   <message name="LoginResponse">
      <part element="tns:LoginOut" name="body"/>
   </message>
   <portType name="CompaniesPort">
      <operation name="Login">
         <input message="tns:Login"/>
         <output message="tns:LoginResponse"/>
      </operation>
   </portType>
   <binding name="CompaniesSoapBinding" type="tns:CompaniesPort">
      <soap:binding style="document" transport="http://schemas.xmlsoap.org/soap/http"/>
      <operation name="Login">
         <soap:operation soapAction="https://morethan/foo/bar/Login" style="document"/>
         <input>
            <soap:body use="literal"/>
         </input>
         <output>
            <soap:body use="literal"/>
         </output>
      </operation>
   </binding>
   <service name="CompaniesService">
      <port binding="tns:CompaniesSoapBinding" name="CompaniesService">
         <soap:address location="https://morethan/foo/bar"/>
      </port>
   </service>
</definitions>