Object structure
Object types are decomposed as atomic, collections, or structured types, as illustrated in
Figure 27.7. In this structure, types shown in italics are abstract types; the types shown in
normal typeface are directly instantiable. We can use only types that are directly instantiable as base types. Types with angle brackets < > indicate type generators. All atomic
objects are user-defined whereas there are a number of built-in collection types, as we see
shortly. As can be seen from Figure 27.7, the structured types are as defined in the ISO
SQL specification (see Section 6.1).