Consistency: This means that only consistent or "valid" data will be allowed to
be entered into the database. In relational terminology, this often means that
the schema of the database has to be applied and maintained at all times. The
main consistency requirement in Neo4j is actually that the graph relationships
must have a start and an end node. Relationships cannot be dangling. Aside
from this, however, the consistency rules in Neo4j will obviously be much
looser, as Neo4j implements the concept of an "optional" schema