Ports are the points of connection that connect the "inside" world of
the component (the process code) with the "outside" world (the
network). Think of a house at, say, 27 Main Street: the
houseowner may say, "Someone is ringing the front door bell", not,
"Someone is ringing the bell at 27 Main Street."
Conversely, the person ringing the bell is seeing 27 Main Street, not
27 Maple Street.
All connections between processes (whether simple or composite) will
have two port names - an upstream one and a downstream one. When
one of the blocks being connected is an IIP or an External Port, only
the process end of the connection will have a port name (upstream or
downstream as appropriate). By definition, an IIP is
always "upstream".
When an arrow is first drawn, the tail end is assigned the name OUT and the head end is IN - unless
these names have already been used for the respective blocks, in which case the user should fill in
names (of course IN and OUT can be modified as desired).
Files and Reports usually show connections, but no port names are
required. Legends may or may not have connections.