@article{Guerra07:sosym,
  author    = {Esther Guerra and Juan de Lara},
  title     = {Event-driven grammars: relating abstract and concrete levels of visual languages},
  journal   = {Software and Systems Modeling, special section on ICGT'04},
  year      = {2007},
  publisher = {Springer},
  pages     = {317-347},
  volume    = {6},
  issue     = {3},
}