Nection boundary

In relational network notation, a nection boundary occurs on the connections between the plural sides of the two nodes of a nection.

In Compact vs. Narrow Notation

 * For nections of compact notation, we make no attempt to locate precisely the boundaries between nections, just identifying "external lines" as the loci of boundaries.
 * The nections of narrow notation have a clear basis for distinguishing boundaries: a line belongs to the same nection as its source, and the boundary is the point at which it connects to its destination node, marked in the notation by an arrowhead.