UML diagrams are an essential tool for planning complex (and even not-so-complex) applications. Properly designed diagrams enable you to document intricate systems in a clearer way than text alone allows. When you use class diagrams as part of your routine software development process, seeing how your classes and database tables should be designed is much easier.
Take full advantage of the OO features in PHP5 to help you rapidly develop applications and establish a code base that's easier to maintain, offers a greater degree of flexibility and extensibility, and reduces the total volume of code required to implement the business requirements.
By separating the software architecture into a business logic layer, like the Individual class, and a data access layer, like the DataManager class, you make it easy to change the underlying data source, table structure, or queries without disrupting the rest of the application. Objects that are responsible for implementing business logic aren't cluttered with the data access mechanism, the presence of which can confuse and obscure the business rules.