The word "connectedness" consistently denotes the significance of an arc, while the word "relationship" denotes the significance of an assertion. This terminological convention emphasizes the distinction between the relationships specified by arcs vs. the relationships specified by assertions. The relationship specified by arcs have no proxies (i.e., they are not and cannot be reified by nodes in situ), even though, in an absolute sense, the relationships specified by arcs are subjects like any other subjects. In discussions of Topic Maps, the word "relationship" is reserved to denote only the relationships that are reified by assertions; it is never used to denote the relationships that are represented (and not reified) by arcs. Arcs are merely components of assertions; they are parts of the backstage machinery of assertions -- machinery which is normally hidden from end users. The machinery of assertion representation is best understood as being capable of reifying in situ all relationships except for the "connectednesses" (arcs) of which the machinery itself consists.

Replaced by edge. Briefly the edge terminology allows the reader to
distinguish between the roles a set of endpoints play in a particular
assertion, represented by the various arcs, and an unreified
relationship between the two nodes. The edge allows us to speak of
reifying such a relationship, as distinguished from the arcs which are
peculiar to a particular assertion.