renchuqiao

### Keybase proof

I hereby claim:

  * I am renchuqiao on github.
  * I am chuqiao (https://keybase.io/chuqiao) on keybase.
  * I have a public key ASDrighlomzOvVFNO-J7A20mxxUmC6g8lBAh1CDhTWjv7wo

To claim this, I am signing this object:

renchuqiao

### Keybase proof

I hereby claim:

  * I am renchuqiao on github.
  * I am chuqiao (https://keybase.io/chuqiao) on keybase.
  * I have a public key ASB1f4L1I8-8NzdF1Zd5-aDqsu2FSqKgB52nISJdI6O4Sgo

To claim this, I am signing this object:

renchuqiao

pragma solidity ^0.4.0;

import './SafeMath.sol';

/**
 * Here is an example of upgradable contract, consisting of three parts:
 *   - Data contract keeps the resources (data) and is controlled by Handlers;
 *   - Handler contract (implements Handler interface) defines operations and provide services. This contract can be upgraded;
 *   - Upgrader contract deals with the voting mechanism and upgrades the Handler contract. The voters are pre-defined by
 *     the contract owner.