CBSA Blockchain Architecture & Design Principles 2 — Questions and Answers
Question 1: Which architectural pattern allows off-chain computations to be verified on-chain without re-executing them?
- Sharding
- Optimistic rollups
- Zero-knowledge proofs (Correct answer)
- State channels
Correct answer: Zero-knowledge proofs
Zero-knowledge proofs let a prover convince a verifier that a computation is correct without revealing inputs or re-running it on-chain.
Question 2: In a UTXO-based blockchain model, what does a transaction consume?
- Account balances directly
- Previous unspent transaction outputs (Correct answer)
- Smart contract state variables
- Merkle tree leaf nodes
Correct answer: Previous unspent transaction outputs
UTXO (Unspent Transaction Output) models require transactions to spend existing outputs and create new ones, unlike account-based models.
Question 3: What is the primary role of a mempool in blockchain architecture?
- Storing finalized block data
- Holding unconfirmed transactions awaiting inclusion (Correct answer)
- Managing validator node identities
- Caching smart contract bytecode
Correct answer: Holding unconfirmed transactions awaiting inclusion
The mempool (memory pool) is a node's local buffer of broadcast transactions not yet included in a block.
Question 4: Which design approach best addresses the blockchain trilemma by sacrificing some decentralization for scalability?
- Increasing block size
- Adding more full nodes
- Delegated Proof of Stake (Correct answer)
- Lengthening block intervals
Correct answer: Delegated Proof of Stake
DPoS concentrates validation among elected delegates, improving throughput and finality at the cost of reduced decentralization.
Question 5: When designing a multi-chain architecture, what purpose does a relay chain serve?
- Executing smart contracts for all parachains
- Providing shared security and cross-chain message passing (Correct answer)
- Storing full transaction history for each connected chain
- Acting as a centralized oracle for all chains
Correct answer: Providing shared security and cross-chain message passing
A relay chain (as in Polkadot) coordinates consensus and provides shared security so individual parachains don't need their own validator sets.
Question 6: Which storage strategy is most appropriate for large files referenced by a blockchain application?
- Storing raw bytes in smart contract state
- Encoding files as base64 in transaction data
- Using IPFS with only the content hash on-chain (Correct answer)
- Embedding files in block headers
Correct answer: Using IPFS with only the content hash on-chain
IPFS provides content-addressed decentralized storage; only the immutable CID (hash) is stored on-chain, keeping blockchain data minimal.
Question 7: What distinguishes a 'light client' from a 'full node' in blockchain architecture?
- Light clients execute all smart contracts locally
- Light clients store only block headers and verify proofs rather than full block data (Correct answer)
- Light clients produce new blocks through mining
- Light clients maintain a complete UTXO set
Correct answer: Light clients store only block headers and verify proofs rather than full block data
Light clients download only block headers and use Simplified Payment Verification (SPV) or proof-based techniques to confirm transactions without full state.
CBSA Blockchain Architecture & Design Principles 2
Which architectural pattern allows off-chain computations to be verified on-chain without re-executing them?