Developing graph database model for department/supplier/items

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I'm currently ramping up on graph databases and to do that am working through a set of questions to learn Cypher. However, I'm not 100% happy with the design I've chosen since I have to match relationships to nodes to make some of the queries work.

I found Neo4j: Suggestions for ways to model a graph with shared nodes but has a unique path based on some property with some suggestions that are relevant, but they involve copying nodes (repeating them) when in fact they do represent the same thing. That seems like an update issue waiting to happen.

My design currently has

(:Dept {name,floor})-[:SOLD {quantity}]->(:Item {name,type})<-[:SUPPLIES {dept,volume)]-(:Company {name,address})

As you can see, to figure out which department a company supplied an item to, I have to check the :SUPPLIES dept property. This leads to somewhat awkward queries - it feels that way to me, anyway.

I've tried other relationships, like having (:Company)-[:SUPPLIES {item,vol}]->(:Dept) but then the problem just shifts to matching :SUPPLIES relationship properties to :Item nodes.

The types of queries I am building are of the nature: Find departments that sell all of the items they are supplied.

Is there some other way to model this that I am overlooking? Or is this sort of relationship, where a supplier is related to two things, an item and a department, just something that doesn't fit the graph model very well?

cypher neo4j
1 Answers

You want to store and query a triangular relationship between :Dept, :Item, and :Company. This can't be accomplished by a linear relationship pattern. Comparing IDs of entities is not the Neo4j way, you would neglect the strengths of a graph database.

(Assuming that I understood your use case scenario) I would introduce an additional node of type :SupplyEvent that has relationships to :Dept, :Item, and :Company. You could also split up :SOLD relationship in a similar way, if you want relations between department, item, and, e.g., a customer.

enter image description here

Now, you can query all companies that supplied which items to which departments (without comparing any IDs):

MATCH (company:Company)<-[:SUPPLIED_FROM]-(se:SupplyEvent)-[:SUPPLIED_TO]->(dept:Dept),
      (se)-[:SUPPLIED]->(item:Item)
RETURN company, item, dept
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