Model properties

If I have an instance data as follow :

<instance>
<root>
  <firstname />
  <lastname />
  <adress />
</root>
</instance>

That's right if I put this in the model ? :

<model>
  <root>
    <firstname required="true" />
    <lastname required="false" />
    <adress required="true" />
  </root>
</model>

The fields firstname and adress are required in the form. Could you correct it if it's not correct ?
Thanks

Rodrigue Vaudan