Musings on the topic of “input shapes” in context of fuzz testing (a powerful automated software testing technique), and why they are important:

I propose that there are two types of inputs: instruction-like and data-like. Of course, there is some overlap where, for example, an instruction contains data, or data contains instructions, but fundamentally, this is what inputs are consumed as by the program. For both of these types, you have three shapes: linear, tree, and directed graph.