What is DApp? Explain the Differences Between Decentralized Applications and Traditional Applications, and Development Architecture

What is DApp?

DApp (Decentralized Application) is an application that runs on blockchain networks, with its backend code running on distributed nodes rather than centralized servers.

Core Characteristics of DApp

According to Ethereum's official definition, a true DApp must meet the following conditions:

Characteristic	Description	Importance
Open Source	Code is publicly transparent, anyone can review	⭐⭐⭐⭐⭐
Decentralized	Data stored on blockchain, no single control point	⭐⭐⭐⭐⭐
Incentive Mechanism	Uses tokens to incentivize network participants	⭐⭐⭐⭐
Consensus Mechanism	Achieves data consistency through algorithms	⭐⭐⭐⭐⭐

DApp vs Traditional Applications

shell
Traditional Application Architecture:
┌─────────────┐      ┌─────────────┐      ┌─────────────┐
│   Frontend  │ ←──→ │   Backend   │ ←──→ │ Centralized │
│  (Web/App)  │      │   Server    │      │  Database   │
│             │      │   (API)     │      │  (MySQL,etc)│
└─────────────┘      └─────────────┘      └─────────────┘
                            ↑
                    Single control point, can be shut down

DApp Architecture:
┌─────────────┐      ┌─────────────┐      ┌─────────────┐
│   Frontend  │ ←──→ │   Smart     │ ←──→ │  Blockchain │
│  (Web/App)  │      │   Contract  │      │   Network   │
│             │      │  (Solidity) │      │(Distributed │
└─────────────┘      └─────────────┘      │   Nodes)    │
                            ↑             └─────────────┘
                    Immutable, runs forever

Detailed Comparison Table

Dimension	Traditional App	DApp
Data Storage	Centralized servers	Blockchain distributed storage
Control	Company/organization controlled	Community governance, no single control
Downtime Risk	Can go down due to server failure	Runs as long as network exists
Data Modification	Administrators can modify	Immutable
User Privacy	Need to trust third parties	Self-controlled data
Censorship Resistance	Easily censored/blocked	Censorship-resistant
Transaction Speed	Fast (millisecond level)	Slow (seconds to minutes)
User Experience	Smooth	Gas fees required, higher barrier
Development Cost	Relatively low	Smart contract audit costs high

DApp Development Architecture

Three-Layer Architecture Model

shell
┌─────────────────────────────────────────┐
│           Frontend Layer                │
│  • React/Vue/Next.js                    │
│  • Web3.js / Ethers.js                  │
│  • Wallet Connection (MetaMask/WalletConnect)│
└─────────────────────────────────────────┘
                    ↓
┌─────────────────────────────────────────┐
│         Interaction Layer               │
│  • Smart Contract ABI                   │
│  • RPC Nodes (Infura/Alchemy)           │
│  • IPFS (Decentralized Storage)         │
└─────────────────────────────────────────┘
                    ↓
┌─────────────────────────────────────────┐
│           Data Layer                    │
│  • Smart Contracts (Solidity/Rust)      │
│  • Blockchain Networks (Ethereum/Polygon)│
│  • The Graph (Indexing Protocol)        │
└─────────────────────────────────────────┘

Core Technology Stack

Frontend Development:

javascript
// Web3.js wallet connection example
import Web3 from 'web3';

const connectWallet = async () => {
  if (window.ethereum) {
    const web3 = new Web3(window.ethereum);
    await window.ethereum.request({ method: 'eth_requestAccounts' });
    const accounts = await web3.eth.getAccounts();
    return accounts[0];
  }
};

// Call smart contract
const contract = new web3.eth.Contract(ABI, contractAddress);
const result = await contract.methods.getBalance().call();

Smart Contract Development:

solidity
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract MyDApp {
    mapping(address => uint256) public balances;
    
    event Deposit(address indexed user, uint256 amount);
    
    function deposit() public payable {
        balances[msg.sender] += msg.value;
        emit Deposit(msg.sender, msg.value);
    }
    
    function getBalance() public view returns (uint256) {
        return balances[msg.sender];
    }
}

Data Indexing (The Graph):

graphql
# subgraph/schema.graphql
type Deposit @entity {
  id: ID!
  user: Bytes!
  amount: BigInt!
  timestamp: BigInt!
}

DApp Development Process

shell
1. Requirements Analysis
   ↓
2. Smart Contract Design
   • Write Solidity code
   • Local testing (Hardhat/Truffle)
   ↓
3. Security Audit
   • Static analysis (Slither)
   • Manual audit
   ↓
4. Contract Deployment
   • Testnet verification
   • Mainnet deployment
   ↓
5. Frontend Development
   • UI/UX design
   • Web3 integration
   ↓
6. Testing & Launch
   • Functional testing
   • Security testing

Mainstream DApp Types

Type	Representative Apps	Characteristics
DeFi	Uniswap, Aave	Decentralized financial protocols
NFT	OpenSea, Blur	Non-fungible token trading
GameFi	Axie Infinity, StepN	Gaming + Finance combination
SocialFi	Lens Protocol	Decentralized social
DAO	Aragon, Snapshot	Decentralized Autonomous Organizations

Interview Key Points

• Understand the essential differences between DApps and traditional applications
• Master basic usage of Web3.js/Ethers.js
• Understand how smart contracts interact with frontend
• Familiar with mainstream wallet connection solutions
• Know security considerations for DApp development
• Understand the role of indexing solutions like The Graph