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Oracles

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.

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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