Neo4j Relationship design

Question

Revisiting Neo4j after a long absence. I have read a lot of articles but still find I have a few questions to get me going again....

1. Bidirectional relationships I have a “connected to”-type scenario where 2 nodes are connected to each other. In fact, the idea is to model a type of flow. However, the flow in both directions is not always the same. I'm uncertain of the best method to use: 1 relationship with 2 properties or 2 distinct relationships?

The former feels like the comfortable choice but then doesn't feel natural in terms of modelling the actual facts – for example: what to call the properties because FlowIn and FlowOut wouldn't make sense when looked at from each nodes' perspective. I also wonder about the performance of properties versus relationships in this case – these values will need to be updated.

2. Representing Time Now I want to take a step further and represent the flow between nodes at specific times or, more accurately, between specific times. So between 2pm and 3pm the flow between #1 and #2 will be x.

How should this be done in an optimal way? Relationship per time frame per connection seems….verbose. Could a timeframe being represented as a node be of value?!

3. Are there any Maximum Flow samples with Cypher out there? Particularly interested in push-relabel max flow problem solving.

Thank you for any advice to might have to offer.

Answer 1

While you have definitely given some thought to your problem the question is a little unclear. This seems to be a question about Graph Data Models. You would like to know how best to organize a model to represent a complex relationship. If you are trying to track the "flow" between two nodes then assign a weight property to a unidirected edge.

Bidirectional relationships should be carefully considered. Neo4j can process them just as fast as unidirectional relationships. A quote from the graphaware about using bidirectional relationships:

Relationships in Neo4j can be traversed in both directions with the same speed. Moreover, direction can be completely ignored. Therefore, there is no need to create two different relationships between nodes, if one implies the other.

I believe your problems can be alleviated by gaining a better understanding of Graph data models. Looking at a few different models and understanding the why will help more than understanding cypher syntax at this point. May I suggest reading this survey by 2 professors at the University of Chile titled "Survey of Graph Database Models." The "Hypernode" model on page 21 may be of particular interest to you since it sounds like you are trying to model a complex cyclic object. From page twenty one;

Hypernodes can be used to represent simple (flat) and complex objects (hierarchical, composite, and cyclic) as well as mappings and records. A key feature is its inherent ability to encapsulate information.

Hopefully that information helps you in your efforts to model a complex relationship.