The Join command launches the export tag process on the Supervisor, where resulting changes are made in the Supervisor’s database. Specifically, all component changes from a join apply to the NiagaraStation (and its child components) that represents that subordinate.
Some additional Join concepts are as follows:
A Join merges export tags and join profile information found in the remote subordinate station with any existing NiagaraStation representation, before making any changes. Existing Niagara proxy points, imported histories, and so on, are not arbitrarily overwritten—instead, merge “intelligence” is applied.
For example, points previously added using the Niagara Proxy Point Manager, and imported histories are typically retained. Such items may co-exist with items made from export tags. Sometimes, a component may be deleted and re-added in a new location. For example, this happens if one or more export tags (that were used in a previous join) were since edited to use a different “station slot path”.
Export tag Joins may be repeated as often as needed. When first adding a subordinate station, you may need to issue many Joins before the NiagaraStation is “finished” in the Supervisor. After engineering is completed for that subordinate, a Join may be infrequently issued, if at all.
In the case of very large jobs with replicated subordinate (JACE) stations, new subordinates may be added and be fully operational after a single Join.
You can issue an export tag Join on a station from either the Supervisor station or from the subordinate station, as needed—you get the same results.
Issuing a Join from the subordinate’s Join Profile Manager ends with a built-in Job Log popup dialog that lists all changes made in the Supervisor as a result of the join. This includes both additions as well as possible deletions, each with related ords. Whereas, a Join issued from the Supervisor silently executes, without an ending popup job log. However, note that the same (join) job log data is available under the Supervisor’s JobService, in the details for that Join job.
A Join issued from the subordinate makes an extra initial connection to the Supervisor. Through a few available JoinProfile properties, this allows even adding a new subordinate in cases where the Supervisor has no “prior knowledge” of a remote host. However, you may issue Joins from a subordinate simply for the convenience of popup job logs.
All Join information about a subordinate station is configured and maintained on that subordinate station—and not the Supervisor. In addition to any distributed export tags, the JoinProfile component under the NiagaraStation that represents the Supervisor is the key holder of important properties. See the next section About the JoinProfile for a summary.