MTAT.03.094 Software Engineering - ut€¢ An analog alarm clock ... • sequence diagrams, communication diagrams, ... MTAT.03.094 / Lecture 07 / © Dietmar Pfahl 2016

MTAT.03.094 / Lecture 07 / © Dietmar Pfahl 2016

MTAT.03.094

Software Engineering

Lecture 07: Architecture

and Design

Dietmar Pfahl

email: [email protected] 2016


Schedule of Lectures (Final)

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: Refactoring

Week 09: Verification and Validation I

Week 10: Guest Lecture I (Testing)

Week 11: Guest Lecture II (Software

Quality Management)

Week 12: Verification and Validation II

Week 13: Agile/Lean Methods

Week 14: Guest Lecture III (Software

Craftsmanship)

Week 15: Course wrap-up, review and

exam preparation

Week 16: no lecture


Acknowledgements

Textbooks/Slides:

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

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

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

• Alexander Serebrenik: Software architecture: Domain-Specific Software Architecture and Architectural Patterns, TU Eindhoven, Lecture 2013

• George Fairbanks: Just Enough Software Architecture, 2012 (Video: https://www.youtube.com/watch?v=x30DcBfCJRI)

• Tutorials by Derek Banas (on YouTube)

https://www.youtube.com/watch?v=x30DcBfCJRI


Structure of Lecture 07

• Why Architecture?

• Terminology: Architect, Architecting, Architecture

• Viewpoints and View Models

• Notation

• Architecture & Design Patterns


Two Telephone Systems


Two Telephone Systems – Pro’s and Con’s

Quality Attribute Landline Phone VoIP (Skype)

Power Outage

Tolerant

++ --

Reliable + -

Scalable - ++

Extendable (new

features)

- ++

Which one is better?


Trade-Offs and Decision-Making

Telephone system for a Fire Brigade Station:


Power Outage

Tolerant

++ --

Reliable + -

Scalable - ++

Extendable (new

features)

- ++

Which one is better?


Trade-Offs and Decision-Making –

Template for capturing design rationales:


• Because <Quality Attribute 1> is more important than <Quality Attribute 2> for this system, we choose <technical (design/architecture) option>, accepting <drawback>


Power Outage

Tolerant

++ --

Reliable + -

Scalable - ++

Extendable (new

features)

- ++


Trade-Offs and Decision-Making – Template


• Because <Power Outage Tolerance> is more important than <Scalability> for this system, we choose a <Landline Phone>, accepting <a higher cost for adding new subscribers>.


Power Outage

Tolerant

++ --

Reliable + -

Scalable - ++

Extendable (new

features)

- ++


Exercise: Analysis of Alarm Clock Architectures

Consider standard alarm clocks that you have seen.

For this exercise, consider each of the following to be representative of an architectural style of alarm clocks:

• An LED alarm clock for a bedroom,

• A LCD travel alarm,

• An analog alarm clock (there are several varieties; choose one).


Architecture Analysis – Purpose

• Assess whether architecture allows system to meet certain quality goals

• e.g. regarding maintainability, modifiability, reliability, performance, ...

• Note: the architecture is assessed, while we hope the results will hold for a system yet to be built

Softwarearchitecture

Softwaresystem

Properties Qualities

implementation

properties?


Architecture Analysis – Techniques

• Questioning techniques:

• how does the system react to various situations;

• often make use of scenarios

• Measuring techniques:

• rely on quantitative measures; architecture metrics, simulation, etc.

• e.g., cohesion & coupling

• Different types of scenarios, e.g. use-cases, likely changes, stress situations, risks, far-into-the-future scenarios

• Which stakeholders to ask for scenarios?

• When do you have enough scenarios?


List of Analysis Methods

• SAAM (Scenario-based Architecture Analysis Method)

• SAAMER (Software Architecture Analysis Method for Evolution and Reusability)

• ATAM (The Architecture Trade-Off Analysis Method)

• SBAR (Scenario-Based Architecture Reengineering)

• ... and many more ...


Let’s Design a Software System!

Source:

George Fairbanks: Just Enough Software Architecture, 2012

CSR: Customer Service Request


Real Story – Rackspace

e.g., scalability


Rackspace: Architecture 1


grep examples:http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_04_02.html







(https://www.usenix.org/legacy/publications/library/proceedings/osdi04/tech/full_papers/dean/dean_html/index.html)

https://www.usenix.org/legacy/publications/library/proceedings/osdi04/tech/full_papers/dean/dean_html/index.html


Rackspace: Quality Attribute Trade-offs


What if you don’t think architecturally?

Remember:All programs have an architecture... But not every architecture suits the problem to be solved by the program!






• Notation



Terminology

• Architect – Person

• Architecting – Process

• Architecture – Product


The Role of the Architect

client,

usersarchitect developers

appearance,

behaviour

construction,

co-operation

architectural

design

visualises prescribes

requirements solutions

createsassess assess


Pre-Architecture Life-Cycle

functionality

agreement

quality

development

stakeholders(few)

Characteristics:

• Iteration mainly on functional requirements

• Few stakeholders involved

• No balancing of functional and quality requirements


Adding Architecture: The Easy Way

architecture

detailed design

implementation

functionality

agreement

quality

development

stakeholders(few)


Architecture in the Life-Cycle

functionality

architecture

quality

agreement

stakeholders(many)

development

Characteristics:

• Iteration on both functional and quality requirements

• Many stakeholders involved

• Balancing of functional and quality requirements


Now, what is ‘Architecting’?


Attribute-Driven Design (ADD)

An architect faces many design issues

These are sub-problems of the overall design problem.

Each issue usually has several alternative solutions (or design options)

The designer makes a design decision to resolve each issue.

Process of ‘Architecting’ = choosing the best options from among the alternatives


Design Issues, Options and Decisions

Example: The type and level of Security in a system

• Security can be decomposed into

• authentication (user recognition),

• authorization (user access to data),

• privacy (encryption of data exchanged on a public network).

• If the architecture is for

• a medical system, then all security sub-issues must be addressed.

• gaming applications, probably not all of them are important, and could be dropped in favor of, e.g., higher performance.


The Bigger Picture – ADD Iterations Example

Top-level:

• usability separate UI 3-tier architecture

Lower-level, within user interface:

• security authenticate users

Lower-level, within data layer:

• availability active redundancy


Once again: Why is documenting design

decisions important?

• Explains why this is a good (better: suitable) architecture

• Emphasizes qualities and criticality with regards to requirements/goals

• Provides context and background

• Prevents repeating (expensive) past steps

Design rationale example:


Now, what is ‘Architecture’?


Architecture in Construction of Buildings


Software Architecture

• Architecture is conceptual.

• Architecture is about fundamental things.

• Architecture exists in some context.

Architectural descriptions are concrete, but the architecture itself is inherently conceptual, and cannot be captured in any (set of) views – nor in the code.

Abstraction !!!

NB: We can only understand qualities in context.


Software Architecture – Definition

Architecture is the fundamental organization of a system embodied in its components, their relationships to each other and to the environment and the principles guiding its design and evolution

(source: IEEE Standard on the Recommended Practice for Architectural Descriptions, 2000)

NB: ’Principles’ includes the explicit identification and mentioning of properties (-> behaviour)

Structure






• Notation



Analogy with Building Architecture

• Overall picture of building (client)

• Front view (client, municipal “beauty” committee)

• Separate picture for water supply (plumber)

• Separate picture for electrical wiring (electrician)

• etc


IEEE Model for Architectural Descriptions

System stakeholder: an individual, team, or organization (or classes hereof) with interests in, or concerns relative to, a system.

View: a representation of a whole system from the perspective of a related set of concerns.

Viewpoint: A viewpoint establishes the purposes (concerns) and audience (stakeholders) for a view and the techniques or methods employed in constructing a view.

Standard:ISO/IEC/IEEE 42010: 2011


Most Common Architectural Views


Philippe Kruchten’s 4+1 View Model

(Scenarios)


Philippe Kruchten’s

4+1 View Model

Logical View:

• Addresses the end user's concerns: captures the functional requirements, i.e., the services the system should provide to its end users.

• Typically, it shows the key abstractions (e.g., classes and associations amongst them).

• In OO systems, this is often at the class level. In complex systems, you may need a package view and decompose the packages into multiple class diagrams. In other paradigms, you may be interested in representing modules and the functions they provide.

• The end result should be a mapping of the required functionality to components that provide that functionality.

Suggested UML notations:

• class diagrams, object diagrams, state charts, and composite structures

Logical View Implementation

View

Process View Deployment View

Scenarios



4+1 View Model

Process View:

• Focuses on behaviour. Addresses needs of system integrators, i.e., people designing the whole system and then integrating the subsystems or the system into a system of systems.

• This view shows tasks and processes that the system has, interfaces to the outside world and/or between components within the system, the messages sent and received, and how performance, availability, fault-tolerance, and integrity are being addressed. The process view also specifies which thread of control executes each operation of each class identified in the logical view.


• sequence diagrams, communication diagrams, activity diagrams, timing diagrams, interaction overview diagrams


View


Scenarios



4+1 View Model

Implementation View:

• Focuses on the organization of the actual software modules in the software-development environment.

• The software is packaged in small chunks (program libraries or subsystems) that can be developed by one or more developers.


• component diagrams, package diagrams


View


Scenarios



4+1 View Model

Deployment View:

• Defines how the various elements identified in the logical, process, and implementation views (networks, processes, tasks, and objects) must be mapped onto the various nodes. (=> Physical View)

• Takes into account the system's non-functional requirements such as system availability, reliability (fault-tolerance), performance (throughput), and scalability.

• This view is primarily for system designers and administrators who need to understand the physical locations of the software, physical connections between nodes, deployment and installation, and scalability.


• deployment diagrams


View


Scenarios



4+1 View Model

Scenarios:

• The scenarios help to capture the requirements so that all the stakeholders understand how the system is intended to be used.

• This view is redundant with the other ones (hence the "+1"), but it plays two critical roles:

• Acts as a driver to help designers discover architectural elements during the architecture design;

• Validates and illustrates the architecture design, both on paper and as the starting point for the tests of an architectural prototype.


• Use case diagrams, activity diagrams


View


Scenarios






• Notation



Three Flavours of Architectural Notations

• Informal

• Hand-drawn figures on the whiteboard

• Plain text

• Semi-Formal: UML

• Formal

• Architecture Description Languages (ADLs)

https://en.wikipedia.org/wiki/Architecture_description_language


Conceptual View Customer, Users


More technical view Developers (same system as on previous slide)


Logical & Implementation View

A University Course Catalogue System

(see full report on course wiki)

Process View

Deployment View


Formal Architecture Description Languages

(ADLs)


Comparison of Notations






• Notation



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 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 MetaHfor missile guidance, navigation, and control systems


Reference Architecture – Example

• Structural viewof Lunar LanderDSSA

• Invariant withexplicit pointsof variation

• Satellite relay

• Sensors


Reference Architecture

MURA: Microsoft Upstream Reference Architecture(Oil & Gas Industry)


DSSAs also include …MURA: Microsoft Upstream Reference Architecture(Oil & Gas Industry)





• Pipes and filters• Data abstraction and

object-oriented organization

• Layered systems• Repositories• Event-based, implicit

invocation• ... and many more






Architectural Patterns


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


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


State-Logic-Display in Web Development


Model-View-Controller (MVC)


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

The class extends the abstract class JFrame (defined in the swing GUI widget toolkit for Java – now succeeded by JavaFX)


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 }


Benefits and Liabilities of MVC

Benefits

Liabilities


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.


The Observer Pattern – Class Diagram

Explanation of Observer Design Pattern’s Class Diagram:

• Subject is the one being observed. It has attach() & detach() methods to add or remove observers respectively. It uses notify() method to publish its changes to observers/subscribers.

• Observers register/attach themselves to the Subject they want to listen to for updates.

• ConcreteObservers are actual Observer objects which treat the notifications they receive from the Subject in their own individual ways.

• ConcreteSubject is the actual Subject object whose state change is notified to multiple Observers.

Source:http://www.javabrahman.com/design-patterns/observer-design-pattern-in-java/


The Observer Pattern – Inbuilt in JDK

Inbuilt Observer Pattern in Java:

Java has an inbuilt Observer pattern implementation using:

• Class java.util.Observable (represents Subject)

• Interface java.util.Observer (represents an Observer)


Concrete Observers in Java need to

implement the Observer interface,

whereas concrete Subject needs to

extend Observable to provide its own

notification logic.

Observersjava.util.Observable <<interface>>java.util.Observer


The Observer Pattern – Example

Implementation (Class Diagram)


Observers



Implementation (Code)


import java.util.Observable;import java.util.Observer;public class Subscriber1 implements Observer{String currentPublisherState;@Overridepublic void update(Observable o, Object arg) {System.out.println("New state received by Subscriber

1:"+arg.toString());this.currentPublisherState=(String)arg;

}}

import java.util.Observable;import java.util.Observer;public class Subscriber2 implements Observer{String currentPublisherState;@Overridepublic void update(Observable o, Object arg) {System.out.println("New state received by Subscriber

2:"+arg.toString());this.currentPublisherState=(String)arg;

}}

import java.util.Observable;public class Publisher extends Observable{public void changeStateTo(String newStateName){this.setChanged();this.notifyObservers(newStateName);

}}

public class Client {public static void main(String args[]){Publisher publisher=new Publisher();publisher.addObserver(new Subscriber1());publisher.addObserver(new Subscriber2());publisher.changeStateTo("assigned");

}}



Implementation (Code)

Lets quickly go through what’s there in Java’s example’s class diagram & corresponding code –

• Publisher is the Subject. It extends java.util.Observable.

• Subscriber1 & Subscriber2 are the Observers. They implement java.util.Observer.

• Client first initiates Publisher. It then adds one instance each of Subscriber1 & Subscriber2 to Publisher’s list of Observers.

• Client then invokes method changeStateTo() with new state value as “assigned”. Internally, Publisher then initiates notifyObservers() with this new state value. Before notifying, Publisher calls setStateChanged() which is a requirement of the java’s observer pattern implementation.

• update() methods of Subscriber1 and Subscriber 2 are called internally by the notifyObservers() method and the new state value received by both in the parameter arg is printed.

Summary:

In the above tutorial we understood what is Observer design pattern and the main


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 Banashttps://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.


Next Lecture

• Date/Time:

• Friday, 21-Oct, 10:15-12:00

• Topic:

• Refactoring (and TDD)

• For you to do:

• Go to Labs next week!

• Start working on Lab Task 4

Documents

MTAT.03.094 Software Engineering - ut€¢ An analog alarm clock ... • sequence diagrams, communication diagrams, ... MTAT.03.094 / Lecture 07 / © Dietmar Pfahl 2016