A set of occurrences and relationships that describes a complex
    data type. For example, a declaration of a record consists of a
    record and some record components. Each record component has a
    type, which may be another record, a pointer to the same record,
    a basic data type such as integer, and so forth. In SCA, the type
    graph connects all these together, with relationships connecting
    the record to its components and the components to their types.