图数据库中的属性允许哪些值(例如Titan、OrientDB、ArangoDB、Neo4J)?

I'm pretty new to the NoSQL scene. I'm trying to understand the capabilities and differences between different graph databases. My understanding is that Orient and Arango use documents as vertices (and edges too, right?). I know that in Titan and Neo that vertices and edges may have properties and that these properties are key:value pairs. It makes sense to me that you might limit the values to primitives ( scene. I'm trying t