MTAT.03.094 Software Engineering · 2015. 10. 30. · MTAT.03.094 / Lecture 07 / © Dietmar Pfahl...

MTAT.03.094 / Lecture 07 / © Dietmar Pfahl 2015

MTAT.03.094

Software Engineering

Lecture 07: Architecture

and Design

Dietmar Pfahl

email: [email protected] Fall 2015


Schedule of Lectures

Week 01: Introduction to SE

Week 02: Requirements Engineering I

Week 03: Requirements Engineering II

Week 04: Analysis

Week 05: Development Infrastructure I

Week 06: Development Infrastructure II

Week 07: Architecture and Design

Week 08: No lecture

Week 09: Refactoring

Week 10: Verification and Validation I

Week 11: Industry Lecture (Testing)

Week 12: Verification and Validation II

Week 13: Agile/Lean Methods

Week 14: Industry Lecture (Agile)

Week 15: Measurement / Course

wrap-up, review and exam

preparation

Week 16: no lecture


Structure of Lecture 07

• What is it? Why bother?

• Terminology: Architect, Architecting, Architecture

• Viewpoints and View Models

• Notation

• Patterns, Styles and DSSAs


Learning from Others:

Patterns, Styles, and DSSAs

Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John

Wiley & Sons, Inc. Reprinted with permission.


How to solve a problem?


Examples of Domains

• Compilers for programming languages

• Consumer electronics

• Electronic commerce system/Web stores

• Video game

• Business applications

• Basic/Standard/“Pro”

We can subdivide, too: • Avionics systems -> Boeing Jets -> Boeing 747-400


Domain-Specific Software Architectures

• A DSSA is an assemblage of software components

• specialized for a particular type of task (domain),

• generalized for effective use across that domain, and

• composed in a standardized structure (topology) effective for building successful applications.

• DSSAs are the pre-eminent means for maximal reuse of knowledge and prior development.


Domain-Specific Software Architectures

A DSSA comprises:

• A reference architecture, which describes a general computational framework for a significant domain of applications

• A component library, which contains reusable chunks of domain expertise, and

• An application configuration method for selecting and configuring components within the architecture to meet particular application requirements

Examples:

• ADAGE for avionics, AIS for adaptive intelligent systems, and MetaH for missile guidance, navigation, and control systems


Reference Architecture – Example

• Structural view of Lunar Lander DSSA

• Invariant with explicit points of variation

• Satellite relay

• Sensors


Reference Architecture


Reference Architecture

MURA: Microsoft Upstream Reference Architecture


DSSAs also include …

MURA: Microsoft Upstream Reference Architecture


Extreme Case of DSSA ...


Product Line Architecture


Product Line Architecture – Why?


How do Product Lines come to be?


Example: Lunar Lander Game


Product Lines in the Lunar Lander Game


Product Lines: Components, Features, Products


Product Lines: Components, Features, Products

???


Better Representation: Variability Model


DSSAs vs. Product Lines


Architectural Patterns


State-Logic-Display (a.k.a. Three-Tier Pattern)


State-Logic-Display in Web Development


Tiers and Layers

Note: The middle tier might be multi-tiered (resulting in an n-tier architecture)


Model-View-Controller (MVC)


MVC Code Example:

CalculatorModel.java

01 // The Model performs all the calculations needed

02 // and that is it. It doesn't know the View exists

03

04 public class CalculatorModel {

05

06 // Holds the value of the sum of the numbers

07 // entered in the view

08

09 private int calculationValue;

11

12 public void addTwoNumbers(int firstNumber, int secondNumber){

13

14 calculationValue = firstNumber + secondNumber;

16 }

17

18 public int getCalculationValue(){

19

20 return calculationValue;

22 }

24 }


MVC Code Example:

CalculatorView.java (1) 01 // This is the View

02 // Its only job is to display what the user sees. It performs no calculations,

03 // but instead passes information entered by the user to whomever needs it.

06

07 import java.awt.event.ActionListener;

09 import javax.swing.*;

10

11 public class CalculatorView extends JFrame{

12

13 private JTextField firstNumber = new JTextField(10);

14 private JLabel additionLabel = new JLabel("+");

15 private JTextField secondNumber = new JTextField(10);

16 private JButton calcButton = new JButton("Calc");

17 private JTextField calcSolution = new JTextField(10);

18

19 CalculatorView(){

20

21 // Sets up the view and adds the components

22

23 JPanel calcPanel = new JPanel();

24

25 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

26 this.setSize(600, 200);

27

28 calcPanel.add(firstNumber);

29 calcPanel.add(additionLabel);

30 calcPanel.add(secondNumber);

31 calcPanel.add(calcButton);

32 calcPanel.add(calcSolution);

33

34 this.add(calcPanel);

35

36 // End of setting up the components --------

38 }

Num1 Num2 +

Calc Sum


MVC Code Example:

CalculatorView.java (2) 39

40 public int getFirstNumber(){

42 return Integer.parseInt(firstNumber.getText());

44 }

45

46 public int getSecondNumber(){

48 return Integer.parseInt(secondNumber.getText());

50 }

51

52 public int getCalcSolution(){

54 return Integer.parseInt(calcSolution.getText());

56 }

57

58 public void setCalcSolution(int solution){

60 calcSolution.setText(Integer.toString(solution));

62 }

63

64 // If the calcButton is clicked execute a method

65 // in the Controller named actionPerformed

66

67 void addCalculateListener(ActionListener listenForCalcButton){

69 calcButton.addActionListener(listenForCalcButton);

71 }

72

73 // Open a popup that contains the error message passed

74

75 void displayErrorMessage(String errorMessage){

77 JOptionPane.showMessageDialog(this, errorMessage);

79 }

81 }

Num1 Num2 +

Calc Sum


MVC Code Example:

CalculatorController.java (1)

01 import java.awt.event.ActionEvent;

02 import java.awt.event.ActionListener;

03

04 // The Controller coordinates interactions

05 // between the View and Model

06

07 public class CalculatorController {

08

09 private CalculatorView theView;

10 private CalculatorModel theModel;

11

12 public CalculatorController(CalculatorView theView, CalculatorModel theModel) {

13 this.theView = theView;

14 this.theModel = theModel;

15

16 // Tell the View that whenever the calculate button

17 // is clicked to execute the actionPerformed method

18 // in the CalculateListener inner class

19

20 this.theView.addCalculateListener(new CalculateListener());

21 }

22

More on the value and advantage of using inner classes (like CalculateListener): http://www.javaworld.com/article/2077411/core-java/inner-classes.html

http://www.javaworld.com/article/2077411/core-java/inner-classes.html






MVC Code Example:

CalculatorController.java (2)

23 class CalculateListener implements ActionListener{

24

25 public void actionPerformed(ActionEvent e) {

26

27 int firstNumber, secondNumber = 0;

28

29 // Surround interactions with the view with

30 // a try block in case numbers weren't

31 // properly entered

32

33 try{

34

35 firstNumber = theView.getFirstNumber();

36 secondNumber = theView.getSecondNumber();

37

38 theModel.addTwoNumbers(firstNumber, secondNumber);

39

40 theView.setCalcSolution(theModel.getCalculationValue());

42 }

43

44 catch(NumberFormatException ex){

45

46 System.out.println(ex);

48 theView.displayErrorMessage("You Need to Enter 2 Integers");

50 }

52 }

54 }

56 }


MVC Code Example:

MVCCalculator.java

01 public class MVCCalculator {

02

03 public static void main(String[] args) {

04

05 CalculatorView theView = new CalculatorView();

06

07 CalculatorModel theModel = new CalculatorModel();

08

09 CalculatorController theController = new CalculatorController(theView,theModel);

10

11 theView.setVisible(true);

12

13 }

14 }


Two Flavors of MVC: Passive Model

• The passive model is employed when one controller manipulates the model exclusively.

• The controller modifies the model and then informs the view that the model has changed and should be refreshed.

• The model is completely independent of the view and the controller, i.e. there is no means for the model to report changes in its state.

• The HTTP protocol is an example of this. There is no simple way in the browser to get asynchronous updates from the server. The browser displays the view and responds to user input, but it does not detect changes in the data on the server.

• Only when the user explicitly requests a refresh is the server interrogated for changes.


Two Flavors of MVC: Active Model

Solution: Observer Design Pattern!


Two Flavors of MVC: Active Model

Figure shows the structure of the active MVC using Observer and how the observer isolates the model from referencing views directly.

Java code example: http://en.wikipedia.org/wiki/Observer_pattern

Observer Pattern:

The observer pattern is a software design pattern in which an object, called the subject, maintains a list of its dependents, called observers, and notifies them automatically of any state changes, usually by calling one of their methods. It is mainly used to implement distributed event handling systems.

ConcreteObserver = ’listener’ in Java swing framework!


Benefits and Liabilities of MVC

Benefits

Liabilities


Patterns, Styles, and DSSAs

Software Architecture: Foundations, Theory, and Practice; Richard N. Taylor, Nenad Medvidovic, and Eric M. Dashofy; © 2008 John

Wiley & Sons, Inc. Reprinted with permission.

• Pipes and filters • Data abstraction and

object-oriented organization

• Layered systems • Repositories • Event-based, implicit

invocation • ... and many more


Design Patterns

• A design pattern is a way of reusing abstract knowledge about a problem and its solution.

• A pattern is a description of the problem and the essence of its solution.

• It should be sufficiently abstract to be reused in different settings.

• Pattern descriptions usually make use of object-oriented characteristics such as inheritance and polymorphism.

ELEMENTS:

Name

A meaningful pattern identifier.

Problem description.

Solution description (might have an example)

Not a concrete design but a template for a design solution that can be instantiated in different ways.

Benefits and Consequences

The results and trade-offs of applying the pattern.


The Observer Pattern

Name: Observer

Problem description

• Situations where multiple displays of state are needed.

Solution description

• Separates the display of object state from the object itself.

• See UML description.

Consequences

• Optimisations to enhance display performance are difficult.


Three Types of

Patterns

Creational patterns:

• Deal with initializing and configuring classes and objects

Structural patterns:

• Deal with decoupling interface and implementation of classes and objects

• Composition of classes or objects

Behavioral patterns:

• Deal with dynamic interactions among societies of classes and objects

• How they distribute responsibility

Observer


Benefits of Design Patterns

• Design patterns enable large-scale reuse of software architectures and also help document systems

• Patterns explicitly capture expert knowledge and design tradeoffs and make it more widely available

• Patterns help improve developer communication

• Pattern names form a common vocabulary

More on Design Patterns: Mini-Tutorials by Derek Banas https://www.youtube.com/playlist?list=PLF206E906175C7E07

https://www.youtube.com/playlist?list=PLF206E906175C7E07

https://www.youtube.com/playlist?list=PLF206E906175C7E07


Further Reading

• Len Bass et al, Sofware Architecture in Practice, 2008 (3rd edition).

• Jan Bosch, Design & Use of Software Architectures, 2000.

• Frank Buschmann et al., Pattern-Oriented Software Architecture: A System of Patterns, 1996. Part II: 2001.

• George Fairbanks: Just Enough Software Architecture, 2012.

• Erich Gamma et al., Design Patterns: Elements of Reusable Object-Oriented Software, 1995.

• C. Hofmeister et al., Applied Software Architecture, 1999.

• Philippe B. Kruchten, The 4+1 view model of architecture, IEEE Software, 12(6):42-50, November 1995.

• Mary Shaw and David Garlan, Software Architecture; Perspectives of an Emerging Discipline, 1995.

• Richard Taylor et al.: Software Architecture, University of California at Irvine, Lecture 2011.

• Ian Sommerville: Software Engineering, 9th edition, 2010. (http://www.softwareengineering-9.com/)

• Hans van Vliet: Software Architecture, Free University of Amsterdam, Lecture 2008.

MTAT.03.094 Software Engineering · 2015. 10. 30. · MTAT.03.094 / Lecture 07 / © Dietmar Pfahl...

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