Two important data types: Node and List

• Node provides generic structure for nodes
  • defined in src/include/nodes/nodes.h
  • specific node types defined in src/include/nodes/*.h
  • functions on nodes defined in src/backend/nodes/*.c
  • Node types: parse trees, plan trees, execution trees, ...
• List provides generic singly-linked list
  • defined in src/include/nodes/pg_list.h
  • functions on lists defined in src/backend/nodes/list.c