NFTs and Marketplaces

What's a token?

Blockchains have a native coin/token that the chain is built with. These coins/tokens are required to execute transactions, send data, are rewards for mining, etc.
But it may be possible to encode additional metadata in the chain which represents a token.

Why use tokens?

Say you want to issue share of stocks to the many co-founders (different percentages) for your new startup company that is yet to be registered
In the Ethereum world, you can represent the shares in the form of “tokens” that can be sold, sold back to the company, transferred, etc.
You can create a “token contract” and deploy it in Ethereum blockchain

Then the tokens can be transferred, sold, etc.

ERC-721 standard

A standard interface for non-fungible tokens, also known as deeds.
Details in

https://eips.ethereum.org/EIPS/eip-721

ERC-721 tokens

Provides basic functionality to track and transfer NFTs
NFTs can represent ownership over digital or physical assets.
NFTs are distinguishable and so the ownership of each one must be tracked separately
NFTs are about managing ownership of general digital assets

ERC-721 use-cases

Physical property — houses, unique artwork
Virtual collectables — unique pictures of kittens, collectable cards
“Negative value” assets — loans, burdens and other responsibilities

Why manage NFT on a blockchain?

Blockchain ensures long-term ownership, until sale.
Provides a trusted record of provenance (forgeries are evident)

ERC-721 Example

Digital art — opensea, foundation
Collector items — NBA top shots
Game items - horses (zed.run), axies
Metaverse - ENS, plots in a virtual land

ERC-721 Interface


      interface ERC721 /* is ERC165 */ {
        event Transfer(address indexed _from, address indexed _to, uint256 indexed _tokenId);
        event Approval(address indexed _owner, address indexed _approved, uint256 indexed _tokenId);
        event ApprovalForAll(address indexed _owner, address indexed _operator, bool _approved);
        function balanceOf(address _owner) external view returns (uint256);
        function ownerOf(uint256 _tokenId) external view returns (address);
        function safeTransferFrom(address _from, address _to, uint256 _tokenId, bytes data) external payable;
        function safeTransferFrom(address _from, address _to, uint256 _tokenId) external payable;
        function transferFrom(address _from, address _to, uint256 _tokenId) external payable;
        function approve(address _approved, uint256 _tokenId) external payable;
        function setApprovalForAll(address _operator, bool _approved) external;
        function getApproved(uint256 _tokenId) external view returns (address);
        function isApprovedForAll(address _owner, address _operator) external view returns (bool);
     }

      /// @dev Note: the ERC-165 identifier for this interface is 0x150b7a02.
      interface ERC165 {
        function supportsInterface(bytes4 interfaceID) external 
        view returns (bool);
     }