Be able to list at least two advantages and two disadvantages of using structures and structure hierarchies. Structures contain not only specifications of primitives and attributes, but also invocations of subordinate structures.
Structures thus exhibit some of the properties of procedures in programming languages.
In particular, just as procedure hierarchy is induced by procedures invoking procedures, structure hierarchy is induced by structures invoking substructures. A structure is a group of elements that provides the necessary information to describe all or part of an object, excluding workstation state and control information. An object is a composite shape and all its data. It is defined in the database by a sequence of elements. The purpose of a structure is to define a coherent geometric model to which can be passed attributes and modeling transformations to substructures.