1. A system for modelling a hardware component of a data processing apparatus in order to generate an output identifying a value of an observable property of the hardware component, comprising: a component model for modelling aspects of the hardware component; feature extraction logic for extending the component model to cause the component model when executing to output one or more features identifying execution behaviour of the component model; and a statistical model arranged to receive said one or more features output by the component model, and to generate said output dependent on said one or more features.