(On Legitimacy of Blockchains - 14)
Some distributed computing frameworks choose data structures that are drastially different from the so-called "blockchain", such as those which belong to the class of DAG (Directed Acyclic Graphs). IOTA and Hedera Hashgraph are typical examples of this, and they are in general way more efficient than blockchains due to the fact that they are not bottlenecking their sequences of transactions under a single chain of events.
These groundbreaking Web3 models, however, oftentimes evince critical flaws in terms of transactional integrity. Since a "transaction history" of a DAG is just one of many alternative paths which are interwoven in a complex web of connections, one can make a reasonable argument that its mode of consensus is significantly less tight and therefore less secure than that of a conventional blockchain. What if a small group of agents dedicate themselves to the creation of a fraudulent line of transactions by approving each other's activities in a fundamentally flawed yet pristinely coordinated manner? How will we be able to prove that this particular chain of events is flawed, while others are not?
There are also types of consensus logic which rely not only on purely computational and/or psychological rules, but also on the nature of physical entities. Distributed file storage ecosystems such as Filecoin, for instance, use PoRep (Proof of Replication) and PoSt (Proof of Spacetime) for the purpose of incentivizing people who keep storing/sharing specific pieces of data in their home computers. One may metaphorically describe this mechanism as some kind of "PoRE (Proof of Real Estate)" because its process of validation involves evidences which claim that the agents do indeed own and have full control over their physical storage spaces.
Another cryptocurrency called Helium (HNT) uses a rather unique method called PoC (Proof of Coverage), in which each participating node is a wireless transmitter (aka "hotspot") that proves its existential legitimacy by covering a specific geographical area within which it is able to send/receive signals. This is a pretty neat way of ensuring that none of the nodes of the network is a fake, zombie account. And just like the aforementioned means of consensus, it can metaphorically equate itself to the concept of "PoRE (Proof of Real Estate)" because literal occupation of space is the primary medium of witnessing the uniqueness of identities here as well.