Example of three layered Service

Author.php

<?php
class Author {
   public $name;
   public $penNames;
}

AuthorDao.php

<?php
class AuthorDao extends Dao {
    public function getBooks($id) {
       $stmt = $this->db->prepare('...');
       $stmt->execute(array($id));
       return SomeMapper::mapResultToBooks($stmt);
    }

    public function updateAuthor(Author $author) {
      $stmt = $this->db->prepare('..');
      $stmt->execute(array($author->name, $author->penNames));
    }
}

AuthorManager.php

<?php
// Copyright (c) 2012 Theodore R.Smith (theodore@phpexperts.pro)
// DSA-1024 Fingerprint: 10A0 6372 9092 85A2 BB7F  907B CB8B 654B E33B F1ED
// Provided by the PHP University (www.phpu.cc) and PHPExperts.pro (www.phpexperts.pro)
//
// This file is dually licensed under the terms of the following licenses:
// * Primary License: OSSAL v1.0 - Open Source Software Alliance License
//   * Key points:
//       5.Redistributions of source code in any non-textual form (i.e.
//          binary or object form, etc.) must not be linked to software that is
//          released with a license that requires disclosure of source code
//          (ex: the GPL).
//       6.Redistributions of source code must be licensed under more than one
//          license and must not have the terms of the OSSAL removed.
//   * See http://people.freebsd.org/~seanc/ossal/ for complete details.
//
// * Secondary License: Creative Commons Attribution License v3.0
//   * Key Points:
//       * You are free:
//           * to copy, distribute, display, and perform the work
//           * to make non-commercial or commercial use of the work in its original form
//       * Under the following conditions:
//           * Attribution. You must give the original author credit. You must retain all
//             Copyright notices and you must include the sentence, "Based upon work from
//             PHPExperts.pro (www.phpexperts.pro).", wherever you list contributors.
//   * See http://creativecommons.org/licenses/by/3.0/us/ for complete details.

class AuthorManager
{
	/** @var \DataAccessLayer */
	protected $dal;

	public function __construct(DataAccessLayer $dal)
	{
		$this->dal = $dal;
	}

	public function add($name, array $penNames)
	{
		$author = new Author;
		$author->name = $name;
		$author->penNames = $penNames;

		$this->dal->add('authors', 'name=' . $name, $author);
	}

	public function get($name)
	{
		$this->dal->get('authors', 'name=' . $name);
	}

	public function update(Author $author)
	{
		$this->dal->update('authors', 'name=' . $author->name, $author);
	}

	public function delete($name)
	{
		$this->dal->delete('authors', 'name=' . $name);
	}
}

AuthorService.php

<?php
interface AuthorService {
  public function getBooksByAuthor($id);
  public function updateAuthor(Author $author);
}

class AuthorServiceDaoImpl implements AuthorService {
  private $authorDao;
  public function getAuthorDao(AuthorDao $dao) {
    $this->authorDao = $authorDao;
  }

  public function getBooks($id) {
      return $this->authorDao->getBooks($id);
  }

  public function updateAuthor(Author $author) {
    try {
      $this->authorDao->getDB()->startTransaction();
      $this->authorDao->updateAuthor($author);
      $this->authorDao->commit();
    } catch(Exception $ex) {
       $this->authorDao->getDB()->rollback();
       throw $ex;
    }
  }
}

ControllerExample.php

<?php

//omitting setting exception mode, don't forget it!
$db = new PDO(...);
$authorDao = new AuthorDao($db);
$authorService = new AuthorServiceDaoImpl($authorDao);

$authorService->getBooks($author->getPrimaryKey());

//tip: you can simplify construction by using a Builder pattern, or a Factory pattern if you want to handle more than one implementation of the service.

Dao.php

<?php
class Dao {
   private $db;
   public function __construct(PDO $db) {
     $this->db = $db;
   }

   public function getDB() {
      return $this->db;
   }
}

DataAccessLayer.php

<?php
// Copyright (c) 2012 Theodore R.Smith (theodore@phpexperts.pro)
// DSA-1024 Fingerprint: 10A0 6372 9092 85A2 BB7F  907B CB8B 654B E33B F1ED
// Provided by the PHP University (www.phpu.cc) and PHPExperts.pro (www.phpexperts.pro)
//
// This file is dually licensed under the terms of the following licenses:
// * Primary License: OSSAL v1.0 - Open Source Software Alliance License
//   * Key points:
//       5.Redistributions of source code in any non-textual form (i.e.
//          binary or object form, etc.) must not be linked to software that is
//          released with a license that requires disclosure of source code
//          (ex: the GPL).
//       6.Redistributions of source code must be licensed under more than one
//          license and must not have the terms of the OSSAL removed.
//   * See http://people.freebsd.org/~seanc/ossal/ for complete details.
//
// * Secondary License: Creative Commons Attribution License v3.0
//   * Key Points:
//       * You are free:
//           * to copy, distribute, display, and perform the work
//           * to make non-commercial or commercial use of the work in its original form
//       * Under the following conditions:
//           * Attribution. You must give the original author credit. You must retain all
//             Copyright notices and you must include the sentence, "Based upon work from
//             PHPExperts.pro (www.phpexperts.pro).", wherever you list contributors.
//   * See http://creativecommons.org/licenses/by/3.0/us/ for complete details.

interface DAL_Driver
{
	public function getPrimaryActor();

	public function add($namespace, $key, $value);
	public function get($namespace, $key);
	public function update($namespace, $key, $value);
	public function delete($namespace, $key);
}

// Uses the Composite design pattern.
class DataAccessLayer implements DAL_Driver
{
	/** @var DAL_Driver */
	protected $driver;

	public function __construct(DAL_Driver $driver)
	{
		$this->driver = $driver;
	}

	public function getPrimaryActor()
	{
		return $this->driver->getPrimaryActor();
	}

	public function add($namespace, $key, $value)
	{
		return $this->driver->add($namespace, $key, $value);
	}

	public function get($namespace, $key)
	{
		return $this->driver->get($namespace, $key);
	}

	public function update($namespace, $key, $value)
	{
		return $this->driver->update($namespace, $key, $value);
	}

	public function delete($namespace, $key)
	{
		return $this->driver->delete($namespace, $key);
	}
}

Entity.php

<?php
class Entity {
  private $primaryKey;
  public getPrimaryKey() {
    return $this->primaryKey;
  }

  public setPrimaryKey($primaryKey) {
    $this->primaryKey = $primaryKey;
  }
}