From this diagram lower-level diagrams are generated. Diagram chasing is a visual method of arguing with abstract "arrows" joined in diagrams. They are similar to another set diagramming technique, Venn diagrams. There are several notations for displaying data-flow diagrams. Use case analysis usually starts by drawing use case diagrams. This idea is used explicitly in the method for drawing phase diagrams. Partitions can be graphically visualized with Young diagrams or Ferrers diagrams. It is used mainly for Venn diagrams and geometry. Venn diagrams are similar to Euler diagrams. Templates can be used to get users started on their diagrams. Statecharts are part of the UML diagrams. UML has introduced significant improvements to the capabilities of sequence diagrams. UML preserves the general form of the traditional state diagrams. Irreducible root systems are named according to their corresponding connected Dynkin diagrams. Piping systems are documented in piping and instrumentation diagrams (P&IDs).