OPC UA Address Space Model - Reference Types

In OPC UA, Standard ReferenceTypes define the relationships between nodes in the address space, specifying the semantics of how nodes are connected, such as hierarchical or non-hierarchical, and whether the relationship is one-way or bidirectional. Understanding this hierarchy can be helpful in troubleshooting issues with browsing a server. For example, as you can see in the below Wireshark browse request capture, the Identifier Numeric showcases what Reference Type the client has requested:

Along with this, a tool such as UA Expert can be helpful to identify what Reference Type a given Node is identified as:

Below is a full diagram and table that outlines the OPC UA Specification for these Reference types.

ReferenceType	NodeId	Description
References	ns=0;i=31	The base ReferenceType from which all other ReferenceTypes derive. It is abstract and symmetric.
NonHierarchicalReferences	ns=0;i=32	Used for references that do not imply a hierarchy. It is abstract and symmetric.
HierarchicalReferences	ns=0;i=33	Used for references that imply a hierarchy. It is abstract.
HasChild	ns=0;i=34	Indicates that the target node is a child of the source node. It is abstract.
Organizes	ns=0;i=35	Indicates that the source node organizes the target node without implying a parent-child relationship.
HasComponent	ns=0;i=47	Indicates that the target node is a component of the source node.
HasOrderedComponent	ns=0;i=49	Similar to HasComponent but indicates that the components have an inherent order.
HasProperty	ns=0;i=46	Indicates that the target node is a property of the source node.
HasSubtype	ns=0;i=45	Indicates that the target node is a subtype of the source node.
HasModellingRule	ns=0;i=37	Associates a node with its modelling rule.
HasTypeDefinition	ns=0;i=40	Indicates that the target node is the type definition of the source node.
HasEncoding	ns=0;i=38	Associates a DataType node with its encoding nodes.
HasDescription	ns=0;i=39	Associates a node with its description.
GeneratesEvent	ns=0;i=41	Indicates that the source node can generate events of the type specified by the target node.
AlwaysGeneratesEvent	ns=0;i=3065	Indicates that the source node always generates events of the type specified by the target node.
Aggregates	ns=0;i=44	Indicates that the target node is an aggregate of the source node. It is abstract.
HasAddIn	ns=0;i=85	Used to add additional functionality to an existing node.
HasEventSource	ns=0;i=36	Indicates that the target node is an event source for the source node.
HasNotifier	ns=0;i=48	Indicates that the target node is a notifier for the source node.