Nefarious Designs has posted part two of their look at the object-oriented functionality, this time, there's a focus on the relationships objects and their friends have.

Following on from my posts "Object-Oriented Concepts" and "Object-Oriented Javascript", I'm going to take a look at OOP in PHP.

In "Part 1: Definition" we took a look at defining objects and classes in PHP. In part 2 I'm going to look at the most important part of any object-oriented system - the relationships.

They look at inheritance, association, aggregation, and references. Code examples are sprinkled liberally to help illustrate the points.