Sometimes, you may want your contracts to interact with the package's previously deployed contracts. Since the deployed addresses exist within the package's .json files, Solidity code cannot directly read contents of these files. So, the flow of making Solidity code access the addresses in .json files is by defining functions in Solidity code to set dependent contract addresses, and after the contract is deployed, call those functions using JavaScript to set the dependent contract addresses.

So you can define your contract code like this:

import "example-truffle-library/contracts/SimpleNameRegistry.sol"; 

contract MyContract { 
  SimpleNameRegistry registry; 
  address public owner; 

  function MyContract { 
    owner = msg.sender; 
  } 

  // Simple example that uses the deployed registry from the package. 
  function getModule(bytes32 name) returns (address) { 
    return registry.names(name); 
  } 

  // Set the registry if you're the owner. 
  function setRegistry(address addr) { 
    if (msg.sender != owner) throw; 

    registry = SimpleNameRegistry(addr); 
  } 
}

This is what your migration should look like:

var SimpleNameRegistry = artifacts.require("example-truffle-library/contracts/SimpleNameRegistry.sol"); 

module.exports = function(deployer) { 
  // Deploy our contract, then set the address of the registry. 
  deployer.deploy(MyContract).then(function() { 
    return MyContract.deployed(); 
  }).then(function(deployed) { 
    return deployed.setRegistry(SimpleNameRegistry.address); 
  }); 
};