A Normal Form Object-Oriented Entity Relationship Diagram

A normal form object-oriented entity relationship (OOER) diagram is presented to address a set of OO data modelling issues, viz. the inability to judge the quality of an OO schema, the presence of inheritance conflicts in ISA hierarchies, the lack of explicit support for different relationship types (m-n, n-ary, recursive etc.) in some OO data models and the lack of general and flexible support for views. Three approaches are described to translate good quality OO schemas from a normal form OOER diagram. The first approach translates OO schemas whose underlying OO data models support the notion of relationship. There are no undesirable redundancies in the translated schemas. The second approach provides for OO data models that do not support the notion of relationship. Some redundancies may arise because of m-n, n-ary relationships, but these can be controlled. The third approach treats each OO schema as an external schema of a conceptual schema represented by a normal form OOER diagram. Redundancies may exist at the external schema level, but no redundancies exist at the conceptual schema level.