Many implementations of smart contracts available in NFT marketplaces today
allow the modification of NFT token attributes, without any specific mechanism
to control the consistency with off-chain metadata. We believe this is a
weakness in overall design of NFTs today. We propose a computation model called
the Asset Proxy NFT that guarantees the consistency between the NFT token
(on-chain) and its corresponding asset metadata (off-chain). In general, the
proposed model can be applied to any type of NFT that requires immutability or
controlled mutability of metadata. A second contribution of this paper is the
notion of the NFT design patterns which recognizes that a coherent framework
for dealing with hybrid assets is required, and that for specific hybrid-asset
deployments, suitable technological components must be utilized under the
framework.Comment: 15 pages, 2 figure