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@XmlTransistant
@XmlRootElement(name = "searchBase")
public class SearchBase {

    protected One one;
    protected Two two;

    //getters & setters
}

@XmlType(propOrder = {
        "one"
        "two"
         "three"
    })

@XmlRootElement(name = "searchExtended")
public class SearchExtended extends Search {

    protected Three three;
    //getters & setters
}

@XmlType(propOrder = {
        "one"
        "two"
    })

@XmlRootElement(name = "search")
public class Search extends SearchBase {
}