OPC UA defines generic Hierarchical References like HasComponent, HasChild, Organizes, etc.

But sometimes, in the systems, we just need a simple non-hierarchical reference without specific semantic, which could be useful to build the infrastructure to link various nodes of a given system.

In VDMA Industrial Joining Technologies - Tightening Working Group, we defined a simple reference called LinksTo to provide a generic way of linking any node.

The LinksTo is a concrete ReferenceType and can be used directly. It is a subtype of NonHierarchicalReferences. The LinksTo reference is symmetric and has no InverseName.
The semantic of this ReferenceType is to link various assets to provide an infrastructure to build the topology of a given system.
This LinksTo reference is defined only to provide basic link between various assets available in the system and there is no restriction on adding additional references in future versions of the specification or in the applications.
The SourceNode of References of this type shall be an Object.
The TargetNode of this ReferenceType shall be an Object
The LinksTo reference is formally defined in the following table.

Table – LinksTo Reference Definition
Attributes Value
BrowseName LinksTo
InverseName
Symmetric True
IsAbstract False
References NodeClass BrowseName Comment
Subtype of the NonHierarchicalReferences defined in OPC 10000-5