olemus
ISO 13584:
iga tipp, milleni võib antud tipust jõuda
tagasisiirdumisega ematipule,
selle ematipule jne
=
any node that can be reached from a given node, by successive traversals of links in the reverse direction. For a given node, its ancestor nodes include all parent nodes, all parent nodes of these parent nodes, etc.

piltlikult
https://callisto.ggsrv.com/imgsrv/FastFetch/UBER1/9781682176771_00186

vt ka
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