The foundation of all the Image_Graph elements
Why a common interface
Because Image_Graph makes heavy use of PHP's built OO (Object Oriented) functionality a common
interface is pretty usefull.
In terms of OO it would be very usefull to use an "interface", but since this is not
implemented in PHP 4 the concept of inheritance is used instead. This means that a lot of
common functionality is put in to a common class, the Image_Graph_Common and
Image_Graph_Element ancestoral classes.
If you are using Image_Graph to create graphs for your website, the answer is pretty simple:
Again in terms of OO it would be very usefull to create these classes as "abstract", but
since this is not implemented in PHP 4 this is implicit. The meaning of abstract classes is
that an instance of the class can not exist at any time (only of descendants), ie newer-ever
create an instance using "new" of these classes.
If you are modifying the source (as according to the GPL) the use of these ancestoral classes
will be to extend all (allmost all) classes using Image_Graph_Common or
Image_Graph_Element. The idea is that every object you will add
(using the Image_Graph_Common::add() method) will HAVE to be
a subclass of Image_Graph_Common.
How do I get on then?
Start by checking the Image_Graph class.