1. A tangible computer readable medium encoded with software, the medium comprising instructions operable to cause data processing apparatus to: receive a core data structure associated with a digital media project being produced, the core data structure including a set of project objects for the digital media project, each project object having characteristics; generate an interface data structure based on the core data structure, the interface data structure being a first instance of the core data structure and including a non-hierarchical structure; display a first display structure in a graphical user interface (GUI) of a digital media authoring program used to manage the project objects of the digital media project being produced, the first display structure being a graphical representation of the interface data structure; receive from a user an input action that selects at least one of the project object characteristics; redefine the interface data structure based on the one or more user-selected project object characteristics, the redefined interface data structure being a second instance of the core data structure and including a hierarchical structure; display a second display structure in the GUI, the second display structure being a graphical representation of the redefined interface data structures; receive from the user an input action to add a project object to the core data structure; identify a category characteristic of the project object to be added to the core data structure; and determine whether the category characteristic is one of the one or more user-selected project object characteristics, and if so, take an action.