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PHP UML Generator
I am trying to understand some php code that is heavily object-oriented and has a MVC structure.. without much luck from just browsing the code.
Is their a tool that can help me, for example by producing some class diagrams, which classes extend which ones, what functions each class has and how they communicate, even in a high level?
If your project is using a known framework, read the docs to understand how it is structured.
Doxygen can help building call graphs and relationships between objects and more if the code is documented.
An IDE such as Eclipse PDT or Komodo will help browsing/viewing.
It probably has an index.php page that will load the code/framework and probably a config.php file to configure it. Reading both of these files will help you figure out where a request starts being processed.
I would recommend http://bouml.free.fr/ - this can create UML diagrams from PHP - very good tool ...