  Attack-defense trees are a novel methodology for graphical security modeling
and assessment. The methodology includes visual, intuitive tree models whose
analysis is supported by a rigorous mathematical formalism. Both, the intuitive
and the formal components of the approach can be used for quantitative analysis
of attack-defense scenarios. In practice, we use intuitive questions to ask
about aspects of scenarios we are interested in. Formally, a computational
procedure, defined with the help of attribute domains and a bottom-up
algorithm, is applied to derive the corresponding numerical values.
  This paper bridges the gap between the intuitive and the formal way of
quantitatively assessing attack-defense scenarios. We discuss how to properly
specify a question, so that it can be answered unambiguously. Given a well
specified question, we then show how to derive an appropriate attribute domain
which constitutes the corresponding formal model. Since any attack tree is in
particular an attack-defense tree, our analysis is also an advancement of the
attack tree methodology.
