Token Registry
The data flow is similar to in the Verifiable Documents, but instead of pointing to a Document Store smart contract, the TradeTrust document will point to a Token Registry smart contract. This smart contract will follow the interface set forth by ERC721, which allows for the document ownership to be part of the immutable ledger.
Since the fingerprint (merkleroot) of the wrapped TradeTrust file is globally uniquely identifying, the Token Registry provides a mapping of these fingerprints (merkleroot) to a title escrow smart contract address. Each fingerprint (merkleroot) can only be registered exactly once, and can have only one smart contract address mapped to it. As such, a pair of (Token Registry, Fingerprint) serves as a universally unique (singularity) registry of ownership for that TradeTrust deed.
Both of these values are mandatory in a valid, wrapped TradeTrust file and its' integrity is also guaranteed by the TradeTrust framework.
TradeTrust supports the construct of assets which can have ownership assigned to them. This is supported using Ethereum smart contracts to keep track of the owner of a particular asset.
An asset is simply defined as the contents of an Electronic Bill of Lading (EBL). It is important to note the distinction between the data contained within a Document describing an asset, and the actual ownership of the asset.
ERC721 Implementation
ERC721 is a only an interface that is widely used for assets registered on the Ethereum or EVM-compatible blockchain, it does not indicate how the smart contract should be implemented.
TradeTrust is using the implementation written by the OpenZeppelin team. We have taken the approach of using a generic ERC721 implementation and composing functionality against that, instead of modifying the implementation directly. This ensures that the originally audited code will not be modified and will preserves its status.
ERC721 specifies that every asset on a registry should have a unique 256 bit ID. For TradeTrust, we will use the keccak256 hash which is the Merkle root of the corresponding TradeTrust document that contains the data representing the EBL.
Singularity Principle
The following conditions apply if our reference implementation is followed:
- Ethereum design guarantees only one copy of a smart contract referenced by a given registry address
- ERC721 smart contract guarantees that each ID can only be registered once with each registry
- Duplicate hash's existence is practically impossible
Hence if we represent an asset by a pair of (Token Registry, Merkleroot), it is universally unique.
What happens to spent or destroyed tokens?
Tokens that have been spent or destroyed will be sent to this address: 0x000000000000000000000000000000000000dEaD. This address is also known as the burnt address.