None of these can model a graph -- the most fundamental relational data structure. Further more, these aren't even "databases" in any meaningful way. The data put into these can change and even be deleted completely at anytime*. No one calls RAM or Read Write Memory a physical database.
* in reality, even if a database is ACID compliant, actual use is not guaranteed in anyway. Your update/delete command can and often will deadlock the entire database, which is fine as long it doesn't violate ACID.