What's the exact purpose of allow extension in PI AF and what are the impact of it being unchecked after templates and elements based on those templates are created
Allow extensions means you can add single attributes to elements deriving from this template. If you don't allow extensions, the attribute list of the derived elements are bound to the template attribute list.
If you uncheck the checkbox after you already defined extended attributes, they will be deleted.
is there a way to trace if someone has unchecked this? and thanks for the above details
I haven't really used it a lot myself, but if the Audit Trail feature is enabled in your system you can right click the AF element template and select "Audit Trail Events". Ref: PI Server
Other than that I don't think there are any more possibilities to see this. What I've done for another project is to export the templates as text (xml) in a custom developed application, store them with version numbers, and then compare the versions to detect what has changed.
AF Audit trail would show this. Though given the impact in terms of disk and resource usage on the SQL Server, I wouldn't recommend using AF Audit trail for this use case. Instead, only give write access to those who need it . That way you reduce the likelihood of an incorrect write, and if it happens you can ask a few specific groups of people.
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