# Creating a relationship between a node and a relationship

I often come across a modeling situation where I want to create a relationship between a node and a relationship. I understand that it can't be done in Neo4j and furthermore isn't a supported graph modeling concept. So, what modeling patterns address this situation? (By the way, surely I'm not the first to inquire about this topic, but I haven't found a discussion.) See image for a concrete example. I have two codes, one contained in one code list and another contained in another code list. A person (Stuart) asserts that the two codes are equivalent, i.e., that the EQUIVALENT_TO relationship exists.

I suspect that the modeling advice would be something like, "Insert a node in the middle of the EQUIVALENT_TO relationship...". OK. But what are the best practices for labeling the node? Typing the two relationships that replaced the one? Any Cypher query gotchas when implementing the pattern?

One way is:
(Stuart)-[:ASSERTS]->(CodeRD)
(Stuart)-[:ASSERTS]->(CodeCB)
(CodeRD)-[:EQUIVALENT]->(CodeCB)

Stuart compares CodeRD and CodeCB and finds they are equivalent.

Thanks for your response. Unfortunately I don't see how that helps. Stuart asserting the codes doesn't do anything useful, as far as I can tell. The assertion is on the equivalence of the two codes. Think something like two codes for the United States, one "US" and another "USA" with an "EQUIVALENT_TO" relationship between them. I would indicate that Stuart asserts the equivalence. Of course I can just have a property on the relationship for Stuart's identifier, but I want to actually link to his node.

If I understand correctly, the equivalence is based on some property value of CodeRD and CodeCB. After creating the nodes, you want to have a way to create the EQUIVALENT relationship? Let me know.

Sorry. I think my simplified diagram was simplified to the point of being misleading. Let me be more precise. The following three nodes exist in the database (among others):

• ( :Code { codeValue: 'RD' } )
• ( :Code { codeValue: 'C8' } )
• ( :Person { name: 'Stuart' } )

The real-life person named 'Stuart', represented by a node has determined that the two Code nodes are equivalent (i.e., mean the same thing), leading to this:

( :Code { codeValue: 'RD' } ) - [:EQUIVALENT_TO] -> ( :Code { codeValue: 'C8' } )

Hi Jim,

As always, modeling graphs is an art that should be weighted always with the search queries you expect to satisfy.

Is there any complication with:

``````( :Code { codeValue: 'RD' } ) - [:EQUIVALENT_TO {asserted_by : 'insert-stuart-identifier-here'}] -> ( :Code { codeValue: 'C8' } )
``````

?

You can always have an index on this property so you can mix IndexSeek with relationship filter on subsequents queries.

Bennu

Bennu (and ameyasoft): Thanks for your comments. I'll try out your recommendations over the next month or so.