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Overview and definitions

  • An oracle is an entity on the blockchain and lives in the oracle state tree in a full node.
  • An oracle is operated by an oracle operator.
  • The oracle operator creates an oracle through posting a oracle register transaction on the chain.
  • The oracle register transaction register an account as an oracle. (One account - one oracle)
  • Any user can query an oracle by posting an oracle query transaction on the chain.
  • The oracle query transaction creates an oracle query object in the oracle state tree.
  • The oracle operator scans the transactions on the blockchain for the oracle query transaction through whatever means. Probably on the operator's own node.
  • The oracle operator responds to the oracle query by posting an oracle response transaction on the chain.
  • The oracle response transaction modifies the oracle query object by adding the response.
  • After the response have been added, the oracle query object is closed, and is now immutable.

Oracle life cycle examples

Oracle state trees

Oracle transactions

Technical aspects of Oracle operations

Oracles have a published API

  • The API defines the format that queries should have. (query_format)
  • The API defines the format answers will have. (response_format)
  • The API defines the ABI version under which the formats should be interpreted.
    • If the ABI version is 0 (?AEVM_NO_ABI):
      • the query and response formats are uninterpreted strings (byte arrays).
      • the queries and responses are treated as strings when called from sophia contracts.
    • For ABI version corresponding to AEVM/FATE:
      • the query and response formats must be type representations, encoded according to the ABI.
      • the queries and responses are interpreted as the types in the format specifications

Oracle responses have a type declaration

  • Types should correspond to types in the smart contract language.
  • There should be incentives to use simple types in oracle answers (boolean, integer).
    • For example, through access cost in smart contracts.

Should oracle responses have restrictions on use?

  • For example, should only the creator of the query be able to use the answer in a smart contract?
  • Should the framework support encryption/decryption of answers?

An oracle query/response has a TTL

  • The actual response will remain on the chain.
  • The response will be pruned from the state tree after a certain number of blocks.
  • The cost of posting the answer should reflect the TTL.
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