Please help me to form a xschema for this data

Question

basically my xml would contain callername,callerpassword,username,password,id as data.
1)All the data input can only be strings.
2)callername and callerpassword is always mandatory(required).
valid options
1)xml can contain callername,callerpassword,username,password
2)xml input can be callername,callerpassword,guid
3)xml input can be callername,callerpassword,username,password,guid.
Any thing other than that is invalid xml for me can anyone help me generate xschema for this data

Answer 1

here you go:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified">
     <xs:element name="callername" type="xs:string"/>
     <xs:element name="callerpassword" type="xs:string"/>
     <xs:element name="data">
          <xs:complexType>
               <xs:sequence>
                    <xs:element ref="callername"/>
                    <xs:element ref="callerpassword"/>
                    <xs:choice>
                         <xs:sequence>
                              <xs:element ref="username"/>
                              <xs:element ref="password"/>
                         </xs:sequence>
                         <xs:choice>
                              <xs:element ref="guid"/>
                         </xs:choice>
                         <xs:sequence>
                              <xs:element ref="username"/>
                              <xs:element ref="password"/>
                              <xs:element ref="guid"/>
                         </xs:sequence>
                    </xs:choice>
               </xs:sequence>
          </xs:complexType>
     </xs:element>
     <xs:element name="guid" type="xs:string"/>
     <xs:element name="password" type="xs:string"/>
     <xs:element name="username" type="xs:string"/>
</xs:schema>