  The non-fungible token (NFT) is an emergent type of cryptocurrency that has
garnered extensive attention since its inception. The uniqueness,
indivisibility and humanistic value of NFTs are the key characteristics that
distinguish them from traditional tokens. The market capitalization of NFT
reached 21.5 billion USD in 2021, almost 200 times of all previous
transactions. However, the subsequent rapid decline in NFT market fever in the
second quarter of 2022 casts doubts on the ostensible boom in the NFT market.
To date, there has been no comprehensive and systematic study of the NFT trade
market or of the NFT bubble and hype phenomenon. To fill this gap, we conduct
an in-depth investigation of the whole Ethereum ERC721 and ERC1155 NFT
ecosystem via graph analysis and apply several metrics to measure the
characteristics of NFTs. By collecting data from the whole blockchain, we
construct three graphs, namely NFT create graph, NFT transfer graph, and NFT
hold graph, to characterize the NFT traders, analyze the characteristics of
NFTs, and discover many observations and insights. Moreover, we propose new
indicators to quantify the activeness and value of NFT and propose an algorithm
that combines indicators and graph analyses to find bubble NFTs. Real-world
cases demonstrate that our indicators and approach can be used to discern
bubble NFTs effectively.
