eosio::singleton, which store data in the database of the blockchain node. Inside the table are
structs. Creating, receiving, modifying or deleting objects is performed in
createoperation for creating tokens in an ABI file:
characters to describe a vector in an ABI-file. The ABI file tables must be accurately described. For example, in the case of cleos when adding a table to a contract with a distorted ABI description data may be lost if there is no error message popping out.
You have to update the ABI file straight after a single change is made in the contract structure, tables, actions or events, as well as after introduction of a new type. In most cases if the ABI file update fails, an error message may not appeared. Such situation is difficult to analyze the work of the contract.