Definition of importation in a model is separated into two parts. Under the IMPORTATION descriptor, one or more models can be defined as submodels. Unique IDs are assigned to those models. Those IDs can then be used as properties of states in the definition of the state hierarchy. A state with a submodel ID as a property becomes an importation state. It is not allowed to define substates for it.
There can be one or more submodel definitions under an IMPORTATION descriptor, and there can be multiple IMPORTATION descriptors in a single model. Each submodel definition is written as ``ModelID = FileName'' on a single line, where ModelID is the user-defined ID of the submodel, and FileName is the name of the file that contains the model to be imported.
For example, the model in Figure 4.12 is written as Table 4.10. sub0 is the ID of the submodel defined in file submodel.des. Designers can choose any ID consisting of characters and numbers, except the pre-defined state properties. The submodel is imported into state B.