AToM   is a tool for modeling, meta-modeling and simulation. It is developed by Prof. Hans Vangheluwe at the MSDL (Modeling, Simulation and Design Lab) of McGill University in Canada in close collaboration with Prof. Juan de Lara at the Autonomous University of Madrid. It allows building and dynamically loading meta-models in its graphical environment. When a meta-model is loaded, the graphical environment is modified according to the allowed entities of the formalism. The user can design models according to the syntax of the formalism. Transformations between models of different formalisms are handled with graph grammars, a powerful formalism to specify transformations in a graphical form. With the support of a simulation engine that implements the semantics of the loaded formalism, AToM can also be used as a simulation environment.
Figure 1.3 shows the main window of AToM with the Entity-Relationship diagrams meta-model loaded in it. The left panel of AToM shows only the buttons of allowed entities. In this case, ``entity'' and ``relation'' are two different kinds of entities in an Entity-Relationship diagram.
Figure 1.4 and Figure 1.5 show the AToM environment with the PetriNet meta-model and the statecharts meta-model loaded in it, respectively. The buttons shown on the left panel vary with the loaded meta-models.
Simulation in AToM is discussed later.