In fact, by looking at the design of the data-binding facilities, we have encountered another example of the Observer pattern. The first example was the MVC pattern that we used to partition our total web application into client and server layers.
The original description of the Observer pattern can be found in the famous Gang of Four (GOF) book (Design Patterns: Elements of Reusable Object-Oriented Software, by Erich Gamma and others), which we can sincerely recommend to read. Although it is already almost fifteen years old, its diagrams are in a pre-UML dialect, and its C++ code examples may not look so familiar, the content is still very valid. For your convenience, if you do not own the book, we found an online version of the Observer pattern, copied from the book, here: http://www.research.ibm.com/designpatterns/example.htm.
The purpose of the Observer pattern as stated by the Gang of Four is:
Define a one-to-many dependency between objects so that when one...