Simply put, Refs define relationships between entities within a haystack database. Refs are Key Value tags which insert an entities unique identifier as the value. From a users perspective, Refs are typically used to refine query results whether it be for analytics or controls.
Most Common Types of Refs:
Refs help you walk the entity tree and determine how points are related to physical spaces, or physical equipment. And in modern uses of haystack, you can also use Refs for mapping relationships between equips.
An example is a Supply Air Temperature point may have an equipRef==@ff4cb980-5e19-41f4-98f3-b34f892d1af. Telling you that this supply air temp is associated with a specific VAV equip.
To learn more about how Refs can be used in filters and queries check out the article below.
Haystack Filters & Queries