Information Modeling and Relational Databases, 2nd Edition

10.5. Nominalization and Objectification

Roughly speaking, objectification or nesting treats a relationship instance as an object in its own right, so it may be talked about like any other object. In UML this is called reification, where instances of an association are objectified as instances of an association class. The basic notion of objectification in ORM and UML was discussed in Chapter 4 and Chapter 9, respectively. Industrial ER typically provides no support for objectification. Some academic versions of ER support objectification, but typically with restrictions (e.g., objectified relationships may have attributes but cannot play in other relationships). This section examines objectification in greater depth, first distinguishing two ...