Data structures in OpenMx are implemented as objects, specifically R S4 objects. The MxModel is the object that contains all of what is necessary in order to specify a structural model. It is primarily a container for other objects while providing the organization that allows the contained objects to refer to one another (see Figure 1). Each MxModel has three slots for metainformation about the model: an internal reference name, a type, and a flag that indicates whether the model can be estimated independently from other models.
