Issue
What are the Linking Rules within the Niagara R2 platform?
Environment
Niagara R2 platform
Cause
Additional information on linking rules to correctly linked objects.
Resolution
In most cases, in order for two properties to be linked, they must use the same data species. In a link, one object's output supplies the value (or trigger) used by the other object with the receiving input. The Link Editor in the JDE enforces this rule when selecting a property on one side of the window to link. An exception to the need for matching data species occurs when linking Gx objects, which have only inputs.
For example, the "binding" input of a GxText object can be linked to any internal (configuration property) of another object, in addition to most output properties. When linked to an internal property, a GxText object displays text showing the value of that property. Unlike "normal" links, Gx object links are considered user-interface ("ui") links, not part of "control logic." Instead, they provide the building blocks of a user interface.
The Link Editor also enforces additional link rules. Many inputs can be linked to a single output as needed ("one-to-many"). For any input property that is already linked, no further link to it is permitted unless the property is a priorityArray type or trigger type (or certain types of Lon properties). Only then is a "many-to-one" link allowed.
External links (between stations) have further restrictions. The following types of external links are not permitted (nor are they shown in the Link Editor):
- Links between prioritizedOutputs and priorityArray input properties.
- Links between properties using triggerType data species.
- Links from a GxText object to an internal property of another object (only inputs or outputs are available).
