Relation

A relation is a typed correspondence between shapes. It specifies which values stand together; a source value can correspond to zero, one, or many target values, and conversely. A span of the form source ← witnesses → target expresses this without making either direction the privileged way to evaluate it.

A relationship associates identified subjects. A mapping computes corresponding values from a source observation; a query derives named results from input collections and parameters. Forward lookup, inverse lookup, and membership testing are distinct capabilities: knowing which pairs belong does not promise an implementation for every mode.

In this graph, a formal relation is an authored predicate between concept notes, such as arranges. That is graph vocabulary. A hosting link or causal dependency does not become a domain relation merely because it connects two nodes.