When a remote device is added to the Device Definition Service (DDS), a facility that represents that device is automatically added to the Facility Service. This is called a Device Facility. The device record resides in the DDS; the facility record resides in the Facility Service.
If the device has subgroupings, a facility representing each subgroup can be added to the Facility Service and linked to the device. The facilities that represent the subgroups are called Linked Facilities. Each linked facility is assigned a facility ordinal (see the Facilities page of the remote device editor).
In contrast to linked facilities where multiple facilities are associated with one device, you can also have a single facility associated with multiple devices. An example would be a compressor station that requires two RTUs.
When a device has a facility linked to it, there is a parent-child relationship between the device facility and the linked facility. The device facility is the parent (top level) facility. The linked facility is the child (subordinate) facility. The parent and child relationship between facilities is important and can be taken advantage of when creating tags and UIS commands. See also Roll-Down Points.
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