Hello Yj1190590,
What if the block creators don't obey the rule? They could use the conflict approvals anyway and that seems better to them because more approvals means better chance to win. And more importantly, there will be no evidence while they did so. Then why does anyone obey the rule for his own benifit?
Block approvers own >50% of the stake. If they approve blocks containing conflicting approvals, that will invite many forking related attacks on the chain including double spend. Approvers can approve another block containing all valid approvals, so they don't benefit by violating the rule. Would a rational stakeholder approve a block that may lead the devaluation of their asset without providing them any benefit? I think not. (This has the same basis as PoS.)
Then how to prevent getting stucked when there are not so many positive users paticipating in the competition if the quorum stake is >50%?
In absence of >50% approvals, no new blocks will be created in those slots. It may not sound that good at first but this is the best policy. It's preferable to not process any transactions than to risk the entire blockchain. Once the connectivity is restored, the stakeholders will approve (or reapprove) the set of blocks offered on top of the previously approved block.
Since the "finality" is not the actual finality, what's the meaning of it? Because the data on chain is still not 100% certain.
All block based chains like Proof-of-Approval including Bitcoin and Ethereum, have the so called probabilistic finality. The newest 'n' blocks in the chains are not considered stable. For Bitcoin, users want that 'n' to be 6 blocks or more. For Proof-of-Approval, it is just 1 block.
Regards,
Shunsai