This document discusses the principle of separation of concerns in software engineering. It provides an overview of separation of concerns and how it relates to breaking programs into distinct and separate areas of responsibility. The document then provides several examples of how to apply separation of concerns through different techniques like horizontal separation by layer (presentation, business, data), vertical separation by module, aspect-oriented programming for cross-cutting concerns, and dependency inversion. The benefits highlighted include increased reusability, maintainability, code quality, and understandability of the application.

1. Separation of Concerns

2. Separation of concerns
About Joshua
 Joshua Thijssen, NoxLogic / Techademy
 Freelance Consultant, Developer, Trainer
 Development in PHP, Python, Perl, C, Java
 jthijssen@noxlogic.nl
 @jaytaph

3. Separation of concerns
About Stephan
 Stephan Hochdörfer, bitExpert AG
 Department Manager Research Labs
 enjoying PHP since 1999
 S.Hochdoerfer@bitExpert.de
 @shochdoerfer

4. Separation of concerns
It is what I sometimes have called the
separation of concerns, which [...] is
yet the only available technique for
effective ordering of one's thoughts.
Edsger W. Dijkstra, "On the role of scientific thought" (1974)

5. Separation of concerns
SoC […] is the process of breaking a
computer program into distinct
features that overlap in functionality
as little as possible.
http://en.wikipedia.org/wiki/Separation_of_concerns

6. Separation of concerns
It`s all about focusing!

7. Separation of concerns
One step a time. Focus on the details!

8. Separation of concerns
<?php
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access_token?...");
$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}
$feed = file_get_contents("http://search.twitter.com/search.json?q=from:ident");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}
foreach($items as $item) {
echo $item['message'];
}

9. Separation of concerns
<?php Controller part!
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access_token?...");
$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}
$feed = file_get_contents("http://search.twitter.com/search.json?q=from:ident");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}
foreach($items as $item) {
echo $item['message'];
}}

10. Separation of concerns
<?php
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access_token?...");
$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}
$feed = file_get_contents("http://search.twitter.com/search.json?q=from:ident");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}
foreach($items as $item) {
echo $item['message'];
View part!
}

11. Separation of concerns
Very unstable. Not safe for changes....

12. Separation of concerns
„Make everything as simple as possible...“

13. Separation of concerns
Establish boundaries

14. Separation of concerns
What are the boundaries?
Presentation Layer

15. Separation of concerns
What are the boundaries?
Presentation Layer
Business Layer

16. Separation of concerns
What are the boundaries?
Presentation Layer
Business Layer
Resource Access Layer

17. Separation of concerns
Isolate functionality, break it apart!

18. Separation of concerns
<?php
namespace AcmeDemoBundleController;
use SymfonyBundleFrameworkBundleControllerController;
use SensioBundleFrameworkExtraBundleConfigurationRoute;
use SensioBundleFrameworkExtraBundleConfigurationTemplate;
class DemoController extends Controller {
/**
* @Route("/", name="_demo")
* @Template()
*/
public function indexAction() {
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");
$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}

19. Separation of concerns
$feed = file_get_contents("http://search.twitter.com/search.json?...");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}
return array('items' => $items);
}
}

20. Separation of concerns
Focus on one responsibility a time!

21. Separation of concerns
<?php
namespace AcmeDemoBundleController;
use SymfonyBundleFrameworkBundleControllerController;
use SensioBundleFrameworkExtraBundleConfigurationRoute;
use SensioBundleFrameworkExtraBundleConfigurationTemplate;
class DemoController extends Controller {
/**
* @Route("/", name="_demo")
* @Template()
*/
public function indexAction() {
$items = array();
Facebook connector
$token = file_get_contents("https://graph.facebook.com/oauth/access_to...");
$feed = file_get_contents("https://graph.facebook.com/ident/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}

22. Separation of concerns
Twitter connector
$feed = file_get_contents("http://search.twitter.com/search.json?...");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}
return array('items' => $items);
}
}

23. Separation of concerns
Interfaces as a contract

24. Separation of concerns
<?php
interface ConnectorInterface {
/**
* Will return an array of the latest posts.
* return array
*/
public function getLatestPosts() {
}
}

25. Separation of concerns
<?php
class FacebookConnector implements ConnectorInterface {
protected $handle;
public function __construct($handle) {
$this->handle = $handle;
}
public function getLatestPosts() {
$items = array();
$token = file_get_contents("https://graph.facebook.com/oauth/access...");
$feed = file_get_contents("https://graph.facebook.com/.
$this->handle."/feed?".$token);
$feed = json_decode($feed, true);
foreach($feed['data'] as $post) {
if('123456789012' === $post['from']['id']) {
$items[] = array(
'date' => strtotime($post['created_time']),
'message' => $post['message']);
}
}
return $items;
}
}

26. Separation of concerns
<?php
class FacebookConnector implements ConnectorInterface {
protected $handle;
public function __construct($handle) {
$this->handle = $handle;
}
public function getLatestPosts() {
$token = $this->getAccessToken();
return $this->readPosts($token);
}
protected function getAccessToken() {
return file_get_contents("https://graph.facebook.com/oauth/access_?...");
}
protected function readPosts($token) {
// read the post, filter all relevant and return them...
}
}

27. Separation of concerns
<?php
class FacebookConnectorV2 extends FacebookConnector {
protected function getAccessToken() {
return md5($this->handle);
}
}
Easy to extend, will not influence
the behaviour of other methods!

28. Separation of concerns
<?php
namespace AcmeDemoBundleController;
use SymfonyBundleFrameworkBundleControllerController;
use SensioBundleFrameworkExtraBundleConfigurationRoute;
use SensioBundleFrameworkExtraBundleConfigurationTemplate;
class DemoController extends Controller {
/**
* @Route("/", name="_demo")
* @Template()
*/
public function indexAction() {
$items = array();
$fb = $this->get('FbConnector');
$items += $fb->getLatestPosts();
$feed = file_get_contents("http://search.twitter.com/search.json?...");
$feed = json_decode($feed, true);
foreach($feed['results'] as $tweet) {
$items[] = array(
'date' => strtotime($tweet['created_at']),
'message' => $tweet['text']);
}

29. Separation of concerns
<?php
namespace AcmeDemoBundleController;
use SymfonyBundleFrameworkBundleControllerController;
use SensioBundleFrameworkExtraBundleConfigurationRoute;
use SensioBundleFrameworkExtraBundleConfigurationTemplate;
class DemoController extends Controller {
/**
* @Route("/", name="_demo")
* @Template()
*/
public function indexAction() {
$items = array();
$fb = $this->get('FbConnector');
$items += $fb->getLatestPosts();
$twitter = $this->get('TwitterConnector');
$items += $twitter->getLatestPosts();
return array('items' => $items);
}
}

30. Separation of concerns
Will improve the testability!

31. Separation of concerns
Will reduce tight coupling!

32. Separation of concerns
Will increase component reuse!

33. Separation of concerns
The value of separation
Why should I do it?

34. Separation of concerns
The value of separation
1. Getting rid of code duplication

35. Separation of concerns
The value of separation
2. Application becomes more stable
and easier to understand

36. Separation of concerns
The value of separation
3. Single responsibility offers clear
extension points

37. Separation of concerns
The value of separation
4. Increases the reusability of
components

38. Separation of concerns
How to separate the concerns?

39. Separation of concerns
How to separate? Horizontal Separation
Presentation Layer
Business Layer
Resource Access Layer

40. Separation of concerns
How to separate? Horizontal Separation
./symfony
|-app
|---cache
|---config
|---Resources
|-src
|---Acme
|-----DemoBundle
|-------Controller
|-------Resources
|---------config
|---------public
|-----------css
|-----------images
|---------views
|-----------Demo
|-----------Welcome
|-------Tests
|---------Controller
|-web

41. Separation of concerns
How to separate? Service Separation
Service Interface Layer
Business Layer
Resource Access Layer

42. Separation of concerns
How to separate? Service Separation
Frontend / UI Webservers
REST API Solr Search Service
Datastore

43. Separation of concerns
How to separate? Vertical Separation
Module A Module B Module C

44. Separation of concerns
How to separate? Vertical Separation
./symfony
|-app
|---cache
|---config
|---Resources
|-src
|---Acme
|-----AdminBundle
|-------Controller
|-------Resources
|-------Tests
|-----ProductsBundle
|-------Controller
|-------Resources
|-------Tests
|-----CustomersBundle
|-------Controller
|-------Resources
|-------Tests
|-web

45. Separation of concerns
How to separate? Vertical Separation
Presentation Presentation Presentation
Layer Layer Layer
Business Business Business
Layer Layer Layer
Resource Resource Resource
Access Layer Access Layer Access Layer

46. Separation of concerns
How to separate? Vertical Separation
./symfony
|-app
|---cache
|---config
|---Resources
|-src
|---Acme
|-----AdminBundle
|-------Controller
|-------Resources
|-------Tests
|-----ProductsBundle
|-------Controller
|-------Resources
|-------Tests
|-----CustomersBundle
|-------Controller
|-------Resources
|-------Tests
|-web

47. Separation of concerns
Cross-cutting concerns?
How to deal with security or logging
aspects?

48. Separation of concerns
How to separate? Aspect Separation
Aspects
Presentation Layer
Business Layer
Resource Access Layer

49. Separation of concerns
How to separate? Aspect Separation
<?php
namespace AcmeProductsAspects;
/**
* @FLOW3Aspect
*/
class LoggingAspect {
/**
* @FLOW3Inject
* @var AcmeLoggerLoggerInterface
*/
protected $logger;
/**
* @param TYPO3FLOW3AOPJoinPointInterface $joinPoint
* @FLOW3Before("method(AcmeProductsModelProduct->delete())")
*/
public function log(TYPO3FLOW3AOPJoinPointInterface $jp) {
$product = $jp->getMethodArgument('product');
$this->logger->info('Removing ' .
$product->getName());
}
}

50. Separation of concerns
Dependency Direction

51. Separation of concerns
Dependency Direction
"High-level modules should not
depend on low-level modules.
Both should depend on
abstractions."
Robert C. Martin

52. Separation of concerns
Inverting Concerns
Presentation
Layer
Business
Layer
Resource
Access Layer

53. Separation of concerns
Inverting Concerns
Presentation UI Presentation
Layer Component Layer
Business Business
Layer Layer
Resource Resource
Access Layer Access Layer

54. Separation of concerns
Inverting Concerns
The goal of Dependency Injection
is to separate the concerns of
obtaining the dependencies from
the core concerns of a component.

55. Separation of concerns
What are the benefits? Let`s recap....

56. Separation of concerns
What are the benefits?
1. Facilitate reusability

57. Separation of concerns
What are the benefits?
2. Ensure the maintainability

58. Separation of concerns
What are the benefits?
3. Increasing the code quality

59. Separation of concerns
What are the benefits?
4. Enables everyone to understand
the application

60. Separation of concerns
What are the benefits?
5. Allows developers to work
on components in isolation

61. Thank you!

62. http://joind.in/6244