PHP Advanced and Object-Oriented Programming 3rd Edition
Related to modularity is abstraction: classes should be defined broadly. This is a common and understandable beginner’s mistake. As an example, instead of designing a class for interacting with a MySQL database, you should make one that interacts with a nonspecific database. From there, using inheritance and overriding, you would define a more particular class for MySQL. This class would look and act like the general database class, but some of its functionality would be customized