Presence of elements based on attribute in XSD

I have xml file like this

<listOfA>
  <a type="1">
    <name></name>
    <surname></surname>
  </a>
  <a type="2">
    <name></name>
    <id></id>
  </a>
</listOfA>

I'd like to make a XSD, so that if value of the attribute "type" is 1, the name and surname elements must be present, and when it's 2, name and id must be there. I tried to generate the XSD in XSD schema generator, but it made the surname and id element minOccurs=0. How could I make it work?