Implementing First Class Relationships in Java

Relationships have been an essential component of OO de-sign since the 90s but OO languages still do not support first-class relationships. Hence, programmers must implement re-lationships in an ad-hoc fashion which results in unnecessar-ily complex code. We have developed a new model for rela-tionships in OO which distinguishes tuples and relationships (mutable sets of tuples) and supports both as first-class con-structs. This paper describes the design of a library for Java which provides this model. 1