Web 3.0 technologies

"Web 3.0" is used in two related senses: the Semantic Web (machine-understandable data) and the decentralised web (users own their data and identity through blockchain). Both rely on the following technologies.

Technologies

Technology	Role
Blockchain	A distributed, tamper-resistant ledger that records transactions without a central authority (Ethereum, Solana)
Smart contracts	Self-executing programs stored on the blockchain that run automatically when conditions are met (Solidity)
Cryptocurrencies and tokens	Native payment and incentive mechanisms; NFTs represent unique digital ownership
Decentralised storage	Files stored across a peer-to-peer network (IPFS, Filecoin, Arweave) instead of one server
Digital wallets and decentralised identity (DID)	MetaMask-style wallets let users sign in and own their identity and assets without a central account
Semantic Web standards	RDF, OWL, SPARQL give data machine-readable meaning
Artificial intelligence and machine learning	Understand data, personalise, and automate
Edge computing and 3D/AR/VR (metaverse)	Immersive, distributed experiences
Oracles	Bring real-world data (prices, weather) safely into smart contracts (Chainlink)

How they enable decentralised applications (dApps)

A dApp has its logic in smart contracts on a blockchain instead of on a company's private server.

User (browser + wallet)
     |  web3.js / ethers.js
Front end (HTML/JS/React)  --->  Smart contract on blockchain  --->  IPFS storage

1. No single point of control: logic runs on many nodes, so there is no central owner who can shut it down or alter it.
2. Trustless transactions: smart contracts enforce rules automatically; consensus (Proof of Stake/Work) validates every action.
3. User ownership: users hold their own keys, data, and assets through wallets, and sign in with a wallet address.
4. Transparency and immutability: all transactions are publicly verifiable and cannot be changed afterwards.
5. Censorship resistance and availability: data and code are replicated across the network.
6. Built-in payments and incentives: tokens allow direct peer-to-peer payments and reward participants.
7. Interoperability: open standards and shared data let dApps and services connect.

Example in JavaScript (ethers.js)

import { ethers } from 'ethers';
const provider = new ethers.BrowserProvider(window.ethereum);   // wallet
const signer   = await provider.getSigner();
const contract = new ethers.Contract(address, abi, signer);      // smart contract
await contract.vote(candidateId);                                 // on-chain action

Examples of dApps: Uniswap (decentralised exchange), Aave (lending), OpenSea (NFT marketplace), ENS (domain names).

Challenges: scalability and transaction fees, user experience, regulation, and security risks in smart contracts.