Just as the node is the most general kind of entity in the Principia Cybernetica network, so
a link is the most general form of relation among nodes. Each link is
a non-reflexive relation from one specific node to another, and thus
representable as a directed arc. Reflexive relations can be constructed
from multiple non-reflexive links.
As with nodes, links come in a variety of types (though at present only one type is implemented). Examples of types of links
include a variety of pragmatic categories, including: simple textual
reference (e.g., looking up the definition of a word that is used in the
definition of another); historical, bibliographical, and biographical
reference; logical implication among concepts; and the historical development of a dialog among a group of authors.
Also included in link types are a variety of semantic categories, to
aid in the process of semantic analysis describe in section semantic,
including : instance-of; case-of; synonym-of; has-part; implies; negates; causes, or the logical flow of an
argument for or against some position.
Heylighen has suggested a general scheme for the development
of semantic relations in terms of fundamental logical and temporal
distinctions.
See also: Joslyn C (1996).: 
Semantic Webs: A Cyberspatial Representational Form for Cybernetics, in: Cybernetics and Systems '96 R. Trappl (ed.), (Austrian Society for Cybernetics).
