schemas/VegCore/VegCore.ERD.mwb: hierarchical tables: made parent pointer NOT NULL so that it can be an identifying column. this requires the root(s) of the hierarchy to be indicated with a self-referential parent pointer rather than a NULL value. this also allows materializing parent elements to arbitrary levels without worrying about hitting the root, because the root's ancestors will simlpy be itself for as many levels as are needed (i.e. materializing several levels up the tree is guaranteed to produce a non-NULL entry for all levels).
schemas/VegCore/VegCore.ERD.mwb: hierarchical tables: made parent pointer NOT NULL so that it can be an identifying column. this requires the root(s) of the hierarchy to be indicated with a self-referential parent pointer rather than a NULL value. this also allows materializing parent elements to arbitrary levels without worrying about hitting the root, because the root's ancestors will simlpy be itself for as many levels as are needed (i.e. materializing several levels up the tree is guaranteed to produce a non-NULL entry for all levels).