  In the field of Model-Driven Engineering, there exist numerous tools that
support various consistency management operations including model
transformation, synchronisation and consistency checking. The supported
operations, however, typically run completely in the background with only input
and output made visible to the user. We argue that this often reduces both
understandability and controllability. As a step towards improving this
situation, we present VICToRy, a debugger for model generation and
transformation based on Triple Graph Grammars, a well-known rule-based approach
to bidirectional transformation. In addition to a fine-grained, step-by-step,
interactive visualisation, VICToRy enables the user to actively explore and
choose between multiple valid rule applications thus improving control and
understanding.
