QGraph permits constraints between an edge and a vertex, as long as they involve comparable types and obey the annotation requirements discussed above, but this functionality is not currently implemented in Proximity. Proximity restricts constraints to either two vertices or two edges; mixing is not allowed.

As we saw above, constraints do not have to use the same attribute on both sides of the expression, as long as the attribute data types can be legally compared. Proximity allows you to compare DBL with FLT and INT, and FLT with INT.