This document describes the use of binary links in topic maps.
This diagram shows how binary associations are related to association templates. An association template is a constraint on the instances that use it as a template. An association that uses a template cannot itself be used as a template for another topic, otherwise all associations can be used as a template providing that all aspects of the association are present. An association template is a subclass of topic and can therefore have names, these names can of course be scoped.
A topic association (A1) has two topic association end points (E1 and E2) which reference three things. The three things referenced from an end are: (T1) a topic that defines the role in relation to the association and the role-playing topic, (T2) a topic that describes the arc between the two topics playing roles in this association and (T3) a topic that defines the type of topic that can be the role-playing topic.
Association (A2) has association (A1) as its template, shown by the template association circle that connects the two (this is itself a predefined topic association). In A2 it is only necessary to define two peices of new information (once the template is specified). These two peices of information are to reference the two topics that play the roles in the binary association. In the diagram (T4) is one of these topics. Note that (T4) is an instance of (T3). Thus meeting the constraint. In addition all the role and arc information is derived from the template association.