  In order to fully unlock the transformative power of distributed ledgers and
blockchains, it is crucial to develop innovative consensus algorithms that can
overcome the obstacles of security, scalability, and interoperability, which
currently hinder their widespread adoption. This paper introduces HybridChain
that combines the advantages of sharded blockchain and DAG distributed ledger,
and a consensus algorithm that leverages decentralized learning. Our approach
involves validators exchanging perceptions as votes to assess potential
conflicts between transactions and the witness set, representing input
transactions in the UTXO model. These perceptions collectively contribute to an
intermediate belief regarding the validity of transactions. By integrating
their beliefs with those of other validators, localized decisions are made to
determine validity. Ultimately, a final consensus is achieved through a
majority vote, ensuring precise and efficient validation of transactions. Our
proposed approach is compared to the existing DAG-based scheme IOTA and the
sharded blockchain Omniledger through extensive simulations. The results show
that IOTA has high throughput and low latency but sacrifices accuracy and is
vulnerable to orphanage attacks especially with low transaction rates.
Omniledger achieves stable accuracy by increasing shards but has increased
latency. In contrast, the proposed HybridChain exhibits fast, accurate, and
secure transaction processing, and excellent scalability.
