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ERC-792 is the V1 arbitration standard. Kleros V2 uses IArbitratorV2 and IArbitrableV2, which remove appeals from the interface for simpler integration. See the Architecture guide for V2 details.

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Overview

ERC-792 defines a standard interface for Arbitrable and Arbitrator contracts. Any Arbitrable contract can be adjudicated by any Arbitrator contract. Arbitrator contracts give rulings; Arbitrable contracts enforce them. This separation allows:
  • Arbitrable developers to not know the internal process of the Arbitrator
  • Arbitrator developers to not know the enforcement logic of the Arbitrable
  • DApps to switch arbitration providers or let users choose their own

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IArbitrable

The Arbitrable contract enforces decisions from the Arbitrator. It must call createDispute and pay the required fee, and it must implement rule to enforce rulings. 
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./IArbitrator.sol";

interface IArbitrable {
    /// @dev To be raised when a ruling is made.
    /// @param _arbitrator The arbitrator giving the ruling.
    /// @param _disputeID ID of the dispute in the Arbitrator contract.
    /// @param _ruling The ruling which was given.
    event Ruling(
        IArbitrator indexed _arbitrator,
        uint256 indexed _disputeID,
        uint256 _ruling
    );

    /// @dev Give a ruling for a dispute.
    ///      Must be called by the arbitrator.
    ///      The purpose of this function is to ensure that the address
    ///      calling it has the right to rule on the contract.
    /// @param _disputeID ID of the dispute in the Arbitrator contract.
    /// @param _ruling Ruling given by the arbitrator.
    ///        Note that 0 is reserved for "refuse to arbitrate".
    function rule(uint256 _disputeID, uint256 _ruling) external;
}

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IArbitrator

The Arbitrator creates disputes, manages appeals, and delivers rulings. 
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./IArbitrable.sol";

interface IArbitrator {
    enum DisputeStatus { Waiting, Appealable, Solved }

    /// @dev Emitted when a dispute is created.
    event DisputeCreation(
        uint256 indexed _disputeID,
        IArbitrable indexed _arbitrable
    );

    /// @dev Emitted when a dispute can be appealed.
    event AppealPossible(
        uint256 indexed _disputeID,
        IArbitrable indexed _arbitrable
    );

    /// @dev Emitted when the current ruling is appealed.
    event AppealDecision(
        uint256 indexed _disputeID,
        IArbitrable indexed _arbitrable
    );

    /// @dev Create a dispute. Must be called by the arbitrable contract.
    /// @param _choices Amount of choices the arbitrator can make (ruling options).
    /// @param _extraData Can be used to define the number of jurors, court, etc.
    /// @return disputeID ID of the created dispute.
    function createDispute(
        uint256 _choices,
        bytes calldata _extraData
    ) external payable returns (uint256 disputeID);

    /// @dev Compute the cost of arbitration.
    /// @param _extraData Can be used to define the number of jurors, court, etc.
    /// @return cost Required ETH to create a dispute.
    function arbitrationCost(
        bytes calldata _extraData
    ) external view returns (uint256 cost);

    /// @dev Appeal a ruling.
    /// @param _disputeID ID of the dispute to appeal.
    /// @param _extraData Can be used to define parameters for the appeal.
    function appeal(
        uint256 _disputeID,
        bytes calldata _extraData
    ) external payable;

    /// @dev Compute the cost of appeal.
    /// @param _disputeID ID of the dispute to appeal.
    /// @param _extraData Can be used to define parameters for the appeal.
    /// @return cost Required ETH to appeal.
    function appealCost(
        uint256 _disputeID,
        bytes calldata _extraData
    ) external view returns (uint256 cost);

    /// @dev Compute the start and end of the dispute's appeal period.
    function appealPeriod(
        uint256 _disputeID
    ) external view returns (uint256 start, uint256 end);

    /// @dev Return the status of a dispute.
    function disputeStatus(
        uint256 _disputeID
    ) external view returns (DisputeStatus status);

    /// @dev Return the current ruling of a dispute.
    function currentRuling(
        uint256 _disputeID
    ) external view returns (uint256 ruling);
}

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extraData Format

The _extraData parameter is used to specify arbitration parameters. In KlerosLiquid (V1), it encodes the subcourt ID and the minimum number of jurors: 
// V1 extraData format
bytes memory extraData = abi.encodePacked(
    uint256(subcourtID),    // Subcourt ID
    uint256(numberOfJurors) // Minimum number of jurors
);

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EIP Reference