

17:02, EEST

June 21, 2021

10:21, EEST

April 3, 2012

Hi,
Your question might be more suited on the OPC Foundation’s forum at https://opcfoundation.org/forum/opc-ua-standard/.
The relevant specification section is https://reference.opcfoundation.org/Core/Part3/6.4.4/#6.4.4.4
ModellingRules mark InstanceDeclarations in a TypeDefinition and control how the instances of the said TypeDefinition should look like. It is a complex topic depending how technical you look at it.
In short Mandatory InstanceDeclarations are “copied” as-is to the instance, i.e. the instance shall have a node with that exact BrowseName. The MandatoryPlaceholder marks that the instance shall have at least one node “like” the placeholder or more specifically that it has at least one target node attached with the same Reference and that the target has the same HasTypeDefinition reference the placeholder had.
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