In the Plutus library, AssetId is defined in module Cardano.Api.Value as
data AssetId = AdaAssetId | AssetId !PolicyId !AssetName
while AssetClass is defined in module Plutus.V1.Ledger.Value as
newtype AssetClass = AssetClass { unAssetClass :: (CurrencySymbol, TokenName) }
, as of the time of writing this question.
Does AssetId and AssetClass have any difference in its meaning. What is the purpose of having two definitions?
Basically, they're the same:
AssetId: Actually, it's not part of Plutus Library. It's part of cardano-node and used mainly in native tokens, for example, when you run the following command, it displays your native tokens:
cardano-cli query utxo --address <address> --testnet-magic 1097911063
AssetClass: this is part of Plutus Library and you can use it in your plutus scripts.
The reason to have two definitions, it's because they're used in different tools.
