As opposed to, say, a Relational DBMS?

What you've done might be very interesting and rewarding to you, but it feels like you wasted three paragraphs in your response with something that falls right into the "just because I could" camp.

Neo4j is neat and underutilized. I think rglullis is just saying, if that's why espeed used it, he could have saved three paragraphs of explanation by just saying that.

I find elegance in simplicity. If you don't need the tabular features of a relational database, why not use a graph DB for relational data? It's like a key value store with directly connected relationships.

This is so much simpler than having to deal with creating tables, DDLs, and migrations:

  >>> g = Graph()
  >>> james = g.vertices.create(name="James")
  >>> julie = g.vertices.create(name="Julie")
  >>> g.edges.create(james, "knows", julie)

But regardless, this is Hacker News where people explore, build, and share new things. I hope we're not moving to a place where that gets admonished.

  * Nodes/Vertices: Person, Topic, Entry
  * Relationships/Edges: Tagged, Authored

  person -- authored --> entry
  entry -- tagged --> topic

The comment system is a separate, generic component.

Marko, the guy who created Gremlin (https://github.com/tinkerpop/gremlin/wiki), just released a Gremlin Tree step (https://github.com/tinkerpop/gremlin/wiki/Tree-Pattern), which makes it really easy to build a threaded comment tree in one quick shot.

If you have a large blog or content system, you can use likes and views to make content recommendations using a basic Gremlin collaborative filtering query:

  // calculate basic collaborative filtering for vertex with user_id
  def rank_items(user_id) {
      m = [:]
      g.v(user_id).out('likes').in('likes').out('likes').groupCount(m)
      m.sort{a,b -> a.value <=> b.value}
      return m.values()
  }