The LML Specification defines three mandatory diagram types, the first being the Action Diagram, which is a diagram representation of the functional components of a system model; the second being the Asset Diagram, which is a diagram representation of the physical components of a system model; and the third being the Spider Diagram, which is a visualization for traceability beyond what a typical hierarchy type diagram can offer. The Physical I/O Diagram is an LML extension, in addition to the three mandatory diagram types, which is a crossover diagram of the functional interactions and relationships between the physical components of a system model.