Traditional Definition (cont.)
DAG with geometry at leaves and transformations and rendering attributes at interior nodes
Optionally grouping operators
Basic event handling mechanisms (interrupts and callbacks (e.g., for picking), polled device registers, logical devices)
Can typically edit pieces of DAG to get dynamic behavior
Secondary use as file format for API interchange
Big traditional users: CAD, Sci/Info Viz, ...
Ex: Core, GKS, PHIGS+, HOOPS