title: Neo4j constraint to prevent orphan nodes
body: <p>A graph in Neo4j can contain an orphan node, that is a node which has no relationships associated with it.</p>
  
  <p>What is a constraint that can be implemented, using Neo4j, to ensure that these types of nodes are not present at any time during graph interaction? If no such constraint exists, how can one go about achieving this requirement?</p>
  
  <p>I am not sure if this counts as a garbage collection topic. If one could set the DBMS to periodically query, and eventually remove such orphan nodes, it would be considered a good solution as well - does Neo4j offer this?</p>
  
  <p>I am working with C# if a solution requires implementation at the application level.</p>