The problem addressed by this thesis is the inability of traditional data models to efficiently support the new database applications of today, such as Computer-Aided Design and multimedia. Traditional data models were designed for specific business type applications, i.e., record keeping (relational) and product assembly (hierarchical). Because of this, their permitted data types, structures, and query languages are specific and therefore limited. New applications require more complex and varied data structures and data types. The flat representation of data by traditional data models results in complex objects being scattered over many relations losing the correspondence between the user's view and database representation. The approach taken was to develop a new object-oriented data model (O-ODM). The object-oriented approach permits both the structure of complex objects and their operations to be specified by the designer, providing a flexibility not available in traditional data models. As a result an object may be modelled closer to the user's view, permitting the application programmer to easily capture its complexity. The result of this thesis is the specification of an object-oriented data definition language (O- ODDL) for the O-ODM. The O-ODDL incorporates the features of a unique object, object classes, inheritance, the covering, and encapsulation. The covering, unique to this O-ODM, is important in that it maps an object in one class to a subset of objects in another, providing the ability to manipulate an object as either a singleton or set. This O-ODM and its O-ODDL provide the constructs necessary to represent the new database applications of today.
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