ISO 9001:2015 clause 4.4 Quality management system and its processes, requires that organizations establish, implement, maintain and continually improve a quality management system, including the processes needed and their interactions.
A useful tool for describing, understanding and analyzing processes, frequently referred to as a "turtle" diagram, was presented by Russ Hopkins, then strategy and business engineer for Ford Supplier Technical Assistance (STA), at several ISO/TS 16949:2002 rollout sessions. His diagram subsequently appeared on page 185 in the ISO/TS 16949:2002 implementation guide published by the AIAG (Automotive Industry Action Group) June 2003. The AIAG subsequently put this publication into the public domain.
This diagram utilizes four legs to represent four questions about a process (with who, with what, how, how many); and, a head and tail to represent the questions about the process inputs (what should we receive) and the process outputs (what should we deliver to meet expectations). The "shell" of the turtle is used for the process name.
The establishment and documentation of a turtle diagram for each of the processes needed for the quality management system might be a good approach for defining process interactions as well because the outputs from each process would be traceable to their input into the other process(s) of the quality management system.
The "Turtle" is now widely used throughout the automotive (ISO/TS 16949), aerospace (AS9100C), food (ISO 22000) and general (ISO 9001) industries.