pragma solidity ^0.4.23;

contract Main{
    IDataProvider dataProvider;
    address public owner;

    constructor(IDataProvider _dataProvider) public {
        owner = msg.sender;
        dataProvider = _dataProvider;
    }

    modifier onlyOwner() {
      require(msg.sender == owner);
      _;
  }

    function getData() public view returns(uint) {
        return dataProvider.getData();
    }

    function setDataProvider(IDataProvider _dataProvider) public onlyOwner {
        dataProvider = _dataProvider;
    }
}


contract IDataProvider {
   function getData() public pure returns(uint);
}

contract DataProvider1 is IDataProvider {

    function getData() public pure returns (uint) {
        return 1;
    }
}

contract DataProvider2 is IDataProvider{

    function getData() public pure returns (uint) {
        return 2;
    }
}