sdd:from
sdd:from points an sdd:Edge at the scene instance it starts from. Its object is a sdd:Node today; later plans extend it to a Port — a named, grounded anchor of the same kind as a raw edge end.
The edge owns its connection rather than deferring to node geometry (spec §4.4): sdd:from names which instance the connection starts at, while sdd:fromAnchor names where on that instance's boundary — the two together are what let a connection hold by construction when the node moves. sdd:to is the mirror predicate for the edge's other end.