The architectural perspective emphasizes the number and abstraction level of the components of a relationship, which together characterize the complexity of the relationship. We will briefly consider three architectural issues: degree (or arity), cardinality, and directionality.
These architectural concepts come from data modeling, and if you have not studied computer science or information systems analysis they might be new to you. These concepts enable relationships to be described precisely and abstractly, which turns out to be critically important when an organizing system that implements relationships among resources needs to change. Application and technology lifecycles have never been shorter than they are now, and vast amounts of new data are being created by increased tracking of online interactions and by all the active resources that are now part of the Internet of Things. Organizing systems built without clear architectural foundations cannot easily scale up in size and scope to handle these new requirements.
The degree or arity of a relationship is the number of entity types or categories of resources in the relationship. This is usually, though not always, the same as the number of arguments in the relationship expression.
Homer Simpson (husband) ⇔ is-married-to ⇔ Marge Simpson (wife)
is a relationship of degree 2, a binary relationship between two entity types, because the “is-married-to” relationship as we first defined ...