alternative to <redefine />

Hi all,
I m new to xsd, I would like to ask if there is a alternative way to nest predefined elements. For instance:
I have defined user element in User.xsd, address element in Address.xsd, phone element in Phone.xsd etc.
in main xsd, I would like to specify what element(s) are nested in user element without redefining (extending) user.

Thanks
ran

P.S.
I use Axis2 ADB binding but it doesn't support complexType extension.