// Xtext stuff. Mapped to grammar
class Parameter  {
    ...
    // Add containment reference to my new EClass
    contains transient ParameterModel paramerModel opposite parameter
}

// My new class, not mapped to the grammar
class ParameterModel {
    // Reference to the container
    container transient Parameter parameter opposite parameterModel

    // My calculated type reference (cloned with proxies)
    contains transient JvmTypeReference rowType // !!! Get replaced by proxy at some point !!!
}