Reference:
ETSI NFV SOL001 v2.5.1:
https://www.etsi.org/deliver/etsi_gs/NFV-SOL/001_099/001/02.05.01_60/gs_NFV-SOL001v020501p.pdf
VNFD related TOSCA type definitions:
https://forge.etsi.org/rep/nfv/SOL001/blob/master/etsi_nfv_sol001_vnfd_2_5_1_types.yaml.