FlyingStone is correct, as is Too Few Stripes.
Except for the additional vital information both are missing: an approach when coded into FMC database has appended information we cannot see ourselves, but the database creators can.
Some waypoints are labelled as IF or IAF waypoint types, it is these that generate the approach logic, similar to Fly-Over or Fly-By in RNAV codings.
Generally speaking, when crew select an approach from FMS, the first waypoint on approach section of waypoint is coded as IAF, somewhere down the line there is one coded IF.
Some random behaviour is sometimes observed when deleting IAF appended information, without crew realising this as they cannot see it, it can be the cause for odd VNAV output afterwards.
Example: DUB ILS 28 can be selected into FMS without transition, the first waypoint coincides with last waypoint of STAR so overwrites the STAR waypoint (speed/alt) and appends its coding (speed/alt) and IAF logic. When crew selects transition from same waypoint in preflight the FMS draws a procedural hold at same waypoint, the initial overfly is still regarded as IAF. Inflight during descent, crew decide to shorten approach (as in practice no procedural hold is flown reaching the waypoint, and crew are advised to route direct to IAF) so crew connects IF to IAF waypoint again. But now as the waypoint selected (same waypoint but from later in the sequence without IAF appended) is used, FMS does not have an IAF anymore, therefore (when descending in VNAV PTH) is transitions to command FLAPS speed as it cannot determine where IAF is. This causes confusion to crew as aircraft does not show a DECEL point anymore and commanded speed in FMS becomes FLAPS speed.
Knowledge of the appended information can be used wisely when entering the route and/or deleting waypoint...