Add ERC: Multi-Owner Non-Fungible Tokens (MO-NFT)

ERCS/erc-7743.md

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+---
+eip: 7743
+title: Multi-Owner Non-Fungible Tokens (MO-NFT)
+description: A new type of non-fungible token that supports multiple owners, allowing shared ownership and transferability among users.
+author: James Savechives (@jamesavechives) <[email protected]>
+discussions-to: https://ethereum-magicians.org/t/discussion-on-eip-7743-multi-owner-non-fungible-tokens-mo-nft/20577
+status: Draft
+type: Standards Track
+category: ERC
+created: 2024-07-13
+---
+
+## Abstract
+This ERC proposes a new standard for non-fungible tokens (NFTs) that supports multiple owners. The MO-NFT standard allows a single NFT to have multiple owners, reflecting the shared and distributable nature of digital assets. This model also incorporates a mechanism for value depreciation as the number of owners increases, maintaining the principle that less ownership translates to more value.
+
+## Motivation
+Traditional NFTs enforce a single-ownership model, which does not align with the inherent duplicability of digital assets. MO-NFTs allow for shared ownership, promoting wider distribution and collaboration while maintaining secure access control. This model supports the principle that some valued information is more valuable if fewer people know it, hence less ownership means higher value.
+
+## Specification
+
+### Token Creation and Ownership Model
+1. **Minting**: When a digital asset is uploaded, a unique MO-NFT is minted, and the uploader becomes the initial owner.
+2. **Ownership List**: The MO-NFT maintains a list of owners. Each transfer adds the new owner to the list while retaining the existing owners.
+3. **Transfer Mechanism**: Owners can transfer the token to new owners. The transfer does not remove the original owner from the list but adds the new recipient.
+
+### Transfer of Ownership
+1. **Additive Ownership**: Transferring ownership adds the new owner to the ownership list without removing the current owners.
+2. **Ownership Tracking**: The smart contract tracks the list of owners for each MO-NFT.
+
+### Value Depreciation
+1. **Value Model**: As the number of owners increases, the value of the MO-NFT decreases to reflect the reduced exclusivity.
+2. **Depreciation Mechanism**: The value depreciation model is defined based on the asset type and distribution strategy. Less ownership equates to more value, following the principle that valued information or assets become less valuable as they become more widely known or accessible.
+
+### Interface Definitions
+The MO-NFT contract implements the following interfaces:
+
+1. **Minting**:
+   - `function mintToken() public onlyOwner returns (uint256);`
+
+2. **Transfer**:
+   - `function transferFrom(address from, address to, uint256 tokenId) public override;`
+   - `function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public override;`
+   - `function safeTransferFrom(address from, address to, uint256 tokenId) public override;`
+
+3. **Ownership Management**:
+   - `function isOwner(uint256 tokenId, address account) public view returns (bool);`
+   - `function getOwnersCount(uint256 tokenId) public view returns (uint256);`
+   - `function balanceOf(address owner) external view override returns (uint256 balance);`
+   - `function ownerOf(uint256 tokenId) external view override returns (address owner);`
+
+### [ERC-721](./eip-721.md) Compliance
+The MO-NFT standard is designed to be compatible with the [ERC-721](./eip-721.md) standard. It implements required functions such as `balanceOf`, `ownerOf`, `safeTransferFrom`, and `transferFrom` from the `IERC721` interface. Approval functions are intentionally disabled due to the multi-owner nature of MO-NFTs, which differs from traditional [ERC-721](./eip-721.md) logic.
+
+The `supportsInterface` function ensures that the MO-NFT declares compatibility with the [ERC-721](./eip-721.md) standard, allowing it to be integrated with existing tools and platforms that support [ERC-721](./eip-721.md).
+
+
+## Rationale
+The rationale behind the design choices in the MO-NFT standard is as follows:
+
+1. **Multi-Ownership Model**: 
+   - We adopted a multi-owner structure to better reflect the nature of digital assets, which can be copied and shared without losing their original form. This model allows for broader distribution and access, enhancing collaboration among multiple owners while retaining a single NFT identity.
+
+2. **Additive Ownership**: 
+   - The decision to allow ownership transfer to be additive (i.e., not removing existing owners) stems from the concept of shared digital assets. This approach ensures that each transfer does not diminish the original owner's rights, enabling a more inclusive ownership model that suits digital content, where multiple stakeholders may have legitimate claims.
+
+3. **Value Depreciation Mechanism**: 
+   - We introduced the value depreciation model based on the concept that the value of information decreases as it becomes more widely accessible. This mechanism incentivizes exclusivity and ensures that as more owners are added, the token's value adjusts accordingly, aligning with real-world economic principles.
+
+4. **[ERC-721](./eip-721.md) Compatibility**: 
+   - We ensured that the MO-NFT standard maintains compatibility with [ERC-721](./eip-721.md) to allow for seamless integration with existing NFT tools, platforms, and marketplaces. This decision was made to leverage the established infrastructure and ecosystem of [ERC-721](./eip-721.md) while extending its capabilities for multi-ownership.
+
+## Backwards Compatibility
+This standard is designed to be backwards compatible with the existing [ERC-721](./eip-721.md) standard. Existing tools and platforms that support [ERC-721](./eip-721.md) should be able to interact with MO-NFTs with minimal modifications.
+
+## Test Cases
+These test cases demonstrate the functionality of MO-NFTs:
+
+1. **Minting an MO-NFT and Verifying Initial Ownership**:
+   - **Input**:
+     - Call `mintToken()` with the sender as the owner.
+   - **Expected Output**:
+     - A new `tokenId` is generated.
+     - The sender becomes the first owner of the token (`isOwner(tokenId, sender)` returns `true`).
+     - The total supply increases by 1 (`totalSupply()` reflects the new count).
+     - The `balanceOf(sender)` increases by 1.
+
+2. **Transferring an MO-NFT and Verifying Additive Ownership**:
+   - **Input**:
+     - Call `transferFrom(sender, receiver, tokenId)` where the sender is an existing owner and `receiver` is not an owner.
+   - **Expected Output**:
+     - The receiver is added to the list of owners (`isOwner(tokenId, receiver)` returns `true`).
+     - The sender remains an owner (`isOwner(tokenId, sender)` still returns `true`).
+     - The total number of owners for the token increases by 1 (`getOwnersCount(tokenId)` reflects the new count).
+     - The `balanceOf(receiver)` increases by 1, and the `balanceOf(sender)` remains the same.
+
+### Additional Detailed Test Case (Optional):
+3. **Failing to Transfer to an Existing Owner**:
+   - **Input**:
+     - Call `transferFrom(sender, existingOwner, tokenId)` where `existingOwner` is already listed as an owner of the token.
+   - **Expected Output**:
+     - The transfer is reverted with an error message `"Recipient is already an owner"`.
+     - The state of the ownership list remains unchanged.
+
+## Security Considerations
+1. **Data Integrity**: Protect the integrity of the ownership list and associated metadata.
+2. **Smart Contract Security**: Follow best practices for smart contract development to prevent vulnerabilities and exploits.
+
+## Copyright
+Copyright and related rights waived via [CC0](../LICENSE.md).