A PAP node is a specialized physical tree node representing an access point, or "AP node"
in the physical graph. An AP represents either a persistent data storage such as a table
where the result data from a source execution unit can be stored in a location where
it can be read by another execution unit, or a server-specific method of transparent
access for a remote datastore. This is analogous to a "C$" staging table in ODI 11g.