  Plasticity modelling has long been based on phenomenological models based on
ad-hoc assuption of constitutive relations, which are then fitted to limited
data. Other work is based on the consideration of physical mechanisms which
seek to establish a physical foundation of the observed plastic deformation
behavior through identification of isolated defect processes ('mechanisms')
which are observed either experimentally or in simulations and then serve to
formulate so-called physically based models. Neither of these approaches is
adequate to capture the complexity of plastic deformation which belongs into
the realm of emergent collective phenomena, and to understand the complex
interplay of multiple deformation pathways which is at the core of modern high
performance structural materials. Data based approaches offer alternative
pathways towards plasticity modelling whose strengths and limitations we
explore here for a simple example, namely the interplay between rate and
dislocation density dependent strengthening mechanisms in fcc metals.
