Metadata Choices (metadata extension)
We have required name and symbol functions in the metadata extension. Every token EIP and draft we reviewed (ERC-20, ERC-223, ERC-677, ERC-777, ERC-827) included these functions.
We remind implementation authors that the empty string is a valid response to name and symbol if you protest to the usage of this mechanism. We also remind everyone that any smart contract can use the same name and symbol as your contract. How a client may determine which ERC-721 smart contracts are well-known (canonical) is outside the scope of this standard.
A mechanism is provided to associate NFTs with URIs. We expect that many implementations will take advantage of this to provide metadata for each NFT. The image size recommendation is taken from Instagram, they probably know much about image usability. The URI MAY be mutable (i.e. it changes from time to time). We considered an NFT representing ownership of a house, in this case metadata about the house (image, occupants, etc.) can naturally change.
Metadata is returned as a string value. Currently this is only usable as calling from web3, not from other contracts. This is acceptable because we have not considered a use case where an on-blockchain application would query such information.