# NFT Technology for Enhanced Global Digital Registers: A Novel Approach to Tokenization
## 8 Experimental Evaluation
### Smart Contract Implementation
#### 8.2.2 Detailed Description of Key Functions  
1. registerItem(string memory _identifier, string memory _metadata) public returns (uint256) Parameters: * _identifier: A unique string identifier for the item (e.g., ISBN, DOI)
* _metadata: A string containing metadata about the item Return value: The token Id of the newly created NFTThis function is the primary entry point for registering new items in the global registry. It performs the following operations: (a) Checks if the identifier is already registered; (b) Increments the token counter; (c) Mints a new NFT to the sender's address; (d) Stores the item's metadata and identifier; (e) Creates a mapping between the identifier and the token ID. Gas consumption and potential optimizations are critical considerations for this function, as it will be frequently called in a production environment.  
* transferOwnership(uint256_tokenId, address_newOwner) public Parameters:
* _tokenId: The unique identifier of the NFT
* _newOwner: The address of the new owner  
This function transfers the ownership of a registered item to a new address. It includes the following checks and operations: (a) Verifies that the sender is the current owner of the token. (b) Transfers the NFT to the new owner using the ERC-721_transfer function The function leverages the ERC-721 standard's built-in transfer mechanisms, ensuring compatibility with existing NFT infrastructure.  
* updateMetadata(uint256_tokenId, string memory_newMetadata) public parameters:
* _tokenId: The unique identifier of the NFT
* _newMetadata: The updated metadata string  
This function allows the current owner of an item to update its associated metadata. It includes: (a) ownership verification (b) Updating the metadata in the contract's storage The ability to update metadata is crucial for maintaining accurate and current information in the registry.  
* verifytlem(string memory_identifier) public view returns (bool) Parameters:
* _identifier: The unique identifier to verify Return value: A boolean indicating whether the item is registered  
This function provides a quick and gas-efficient way to check if an item is registered in the system. It simply checks if the identifier has an associated token ID.  
* getItemDetails(uint256_tokenId) public view returns (string memory, string memory, address) Parameters:
* _tokenId: The unique identifier of the NFT return values:
* The item's identifier
* The item's metadata
* The current owner's address  
This function retrieves comprehensive information about a registered item. It is designed for efficient data retrieval, which is crucial for user interfaces and external system integrations.  
* batchRegister(string[] memory_identifiers, string[] memory_metadataList) public Parameters:
* _identifiers: An array of unique identifiers
* _metadataList: A corresponding array of metadata strings  
This function allows for the registration of multiple items in a single transaction, offering gas savings for bulk operations. It includes: (a) Validation of input array lengths (b) Iterative registration of each item using the registerItem function. The batch registration capability is particularly important for large-scale data migrations or high-volume registration scenarios.