**Links** describe relationships between Arvados objects, and from objects to primitives.
Links are directional: each metadata object has a tail (the "subject" being described), class, name, properties, and head (the "object" that describes the "subject"). A Link may describe a relationship between two objects in an Arvados database: e.g. a _permission_ link between a User and a Group defines the permissions that User has to read or modify the Group. Other Links simply represent metadata for a single object, e.g. the _identifier_ Link, in which the _name_ property represents a human-readable identifier for the object at the link's head.
**Links** describe relationships between Arvados objects, and from objects to primitives.
Links are directional: each metadata object has a tail (the "subject" being described), class, name, properties, and head (the "object" that describes the "subject"). A Link may describe a relationship between two objects in an Arvados database: e.g. a _permission_ link between a User and a Group defines the permissions that User has to read or modify the Group. Other Links simply represent metadata for a single object, e.g. the _identifier_ Link, in which the _name_ property represents a human-readable identifier for the object at the link's head.