Software Engineering I (02161) activity diagram only shows one perspective of the dynamic aspect of...

Software Engineering I (02161)Week 5

Assoc. Prof. Hubert Baumeister

Informatics and Mathematical ModellingTechnical University of Denmark

Spring 2011

c©2011 H. Baumeister (IMM) Software Engineering I (02161) Spring 2011 5 / 65

Recap

Recap: Class Diagrams

Class diagram: Visualize OO programs (i.e. based on OOprogramming languages)→ However, have more abstract language

Classes: combines data and methods related to a commonaspect (e.g. Person, Address, Company, . . . )Generalization between classes (corresponds to inheritance)Association between classes

UnidirectonalAssociations vs. attributes

Multiplicities and how to implement them: 0..1, 1, *Bi-directionalQualifed assocations: Corresponds to the use of maps ordictionariesAggregation and Composition


Activity Diagrams

Activity Diagram: Business Processes

Describe the context of the systemHelps finding the requirements of a system

modelling business processes leads to suggestions for possiblesystems and ways how to interact with themSoftware systems need to fit in into existing business processes

Ian Sommerville, Software Engineering – 9, 2010


Activity Diagrams

Activity Diagram Example Workflow


Activity Diagrams

Activity Diagram Example Operation


Activity Diagrams

UML Activity Diagrams

Focus is on control flow and data flowGood for showing parallel/concurrent control flowPurpose

Model business processesModel workflowsModel single operations

Literature: UML Distilled by Martin Fowler


Activity Diagrams

Activity Diagram Concepts

ActionsAre atomicE.g Sending a message, doing some computation, raising anexception, . . .

UML has approx. 45 Action typesConcurrency

Fork: Creates concurrent flowsCan be true concurrencyCan be interleaving

Join: Synchronisation of concurrent activitiesWait for all concurrent activities to finish (based on token semantics)

DecisionsNotation: Diamond with conditions on outgoing transitionselse denotes the transition to take if no other condition is satisfied


Activity Diagrams

Activity Diagrams Execution


Activity Diagrams

Swimlanes / Partitions

Swimlanes show who is performing an activity


Activity Diagrams

Objectflow example


Activity Diagrams

Data flow and Control flow

Data flow and control flow are shown:

Order MakePayment

ReceiveInvoice

Control flow can be omitted if implied by the data flow:

Order MakePayment

ReceiveInvoice


Activity Diagrams

Use of Activity Diagrams

Emphasise on concurrent/parallel executionRequirements phase

To model business processes / workflows to be automatedDesign phase

Show the semantics of one operationClose to a graphic programming language

An activity diagram only shows one perspective of the dynamicaspect of the system

Use several activity diagrams and don’t put everything into onediagram


From Requirements to Design: CRC Cards

Activities in Software Developement

Understand and document what kind of the software the customerwants→ Requirements Analysis

Determine how the software is to be built→ Design

Build the software→ Implementation

Validate that the software solves the customers problem→ Testing→ Verification→ Evaluation: e.g. User friendlieness



From Requirements to Design: Solution

Design process1 The terms in the glossary give first candidates for classes,

attributes, and operations2 Take one use cases

a Take one main or alternative scnearioi Realize that scenario by adding new classes, attributes, associations,

and operations so that you design can execute that scenario(ii implement the design) (in case of an agile software development

process)

b Repeat step a with the other scenarios of the use case

3 Repeat step 2 with the other use cases

Techniques that can be usedGrammatical analysis of the text of the scenario→ nouns are candidate for classes and attributes; verbs are candidates

for operations, and adjectives are candidates for attributesCRC cards (= Class Responsibility Collaboration cards)



Introduction CRC Cards

CRC cards were developed by Ward Cunningham in the late 80’sCan be used for different purposes

Analyse a problem domainDiscover object-oriented designs

Learn to think objects→ Objects

have structure and behaviour→ both need to be considered at the same time

Literaturehttp://c2.com/doc/oopsla89/paper.htmlMartin Fowler: UML Destilled pages 62—63


http://c2.com/doc/oopsla89/paper.html


CRC Card

ClassCan be an object of a certain typeCan be the class of an objectCan be a component of a systemIndex cards are used to represent classes (one for each class) (Iuse A6 paper instead of index cards)

ResponsibilitiesCorresponds roughly to operations and attributesSomewhat larger in scope than operations”do something””know something”

CollaborationsWith whom needs this class to collaborate to realize itsresponsibilities



CRC Card Template

A larger examplehttp://c2.com/doc/crc/draw.html


http://c2.com/doc/crc/draw.html


Process I

Starting pointList of use-cases scenarios

Should be as concrete as possible

A group of up to 2–6 peopleBrainstorming

Initial set of Classes (just enough to get started)Assign Classes to persons

Execute ScenariosSimulate how the computer would execute the scenarioEach object/class is represented by one personThis person is responsible for executing a given responsibility

This is done by calling the responsibilities of other objects/persons hecollaborates with

objects/classes can be createdresponsibilitites can be addedcollaborations can be added



Library Example: Detailed Use Case Check Out Book

Name: Check Out BookDescription: The user checks out a book from the libraryActor: UserMain scenario:

1 A user presents a book for check-out at the check-out counter2 The system registers the loan

Alternative scenarios:The user already has 10 books borrowed

2a The system denies the loanThe user has one overdue book

2b The system denies the loan



Example II

Set of initial CRC cardsLibrarien

The object in the system that fulfills User requests to check out, checkin, and search for library materials

BorrowerThe set of objects that represent Users who borrow items from thelibrary

BookThe set of objects that represent items to be borrowed from the library

Use case Check out book main scenario”What happens when Barbara Stewart, who has no accrued fines andone outstanding book, not overdue, checks out a book entitledEffective C++ Strategies+?”



Library Example: All CRC cards



Process: Next Steps

Review the resultGroup cards

by collaborationsshows relationship between classes

Check responsibilitiesCheck correct representation of the domainRefactor if needed

Transfer the resultUML class diagrams

Responsibilities map to operations and attributes/associationsCollaborations map to associations and dependencies

The executed scenarios to UML interaction diagrams



Example: Class Diagram (so far)

0..1 *

Borrower

canBorrow

Book

isOverduecheckOut(b:Borrower)calculateDueDate

Librarien

checkOutBook(b:Book)

Date

compare(d:Date)

* *

0..1 dueDate



Example: Sequence Diagram for Check-out book

Check Out Book Realization



Summary

Further scenarios give more detailThe scenarios are now quite easy to implementCRC process can be repeated on a more detailed level, e.g., todesign the database interaction, or user interfaceHelps one to think in objects (structure and behaviour)Humans playing objects help to get a better object-oriented designas it helps delegating responsibilities


Sequence Diagrams

Interaction Diagrams

PurposeDescribes how objects collaborate in some behaviour

TypesSequence Diagrams

1990’s: Message Sequence Charts (MSCs) used in TelCo-industry

Communication DiagramsTiming Diagrams


Sequence Diagrams

Example Sequence Diagrams


Sequence Diagrams

Example Communication Diagrams


Sequence Diagrams

Use of Sequence Diagrams

Usually a single scenarioBut can be extended to include several interactions

→ Executable UML / UML as a programming languageClass/object interactions

Express message exchange between objectsDesign message exchangeGet an overview of existing systems

Use Case ScenariosIllustrate a concrete scenario of a use caseUseful for design/documentation (Analysis, design, andreengineering)


Sequence Diagrams

Sequence Diagram Concepts


Sequence Diagrams

Creation and deletion of participants


Sequence Diagrams

Arrow types

a:A b:B

async call

sync call

return


Sequence Diagrams

Interaction Frames Example

Realising an algorithm using a sequence diagram

public void dispatch() {for (LineItem lineItem : lineItems) {if (lineItem.getValue() > 10000) {careful.dispatch();

} else {regular.dispatch();

}}if (needsConfirmation()) {messenger.confirm();

}}


Sequence Diagrams

Realisation with Interaction Frames


Sequence Diagrams

Interaction Frame Operators I


Sequence Diagrams

When to use sequence diagrams

Useful to visualize complex interactions between objectsVisualize the control flow in an object-oriented systemReverse Engineering but also Forward Engineering

Useful to describe Use Case scenariosSequence diagrams are less useful for describing algorithms→ Use state machines to show the behaviour of a single object across

several scenarios→ Use activity diagrams to show the behaviour of across many

objects and threads


Object-orientation: Centralized vs DecentralizedControl/Computation

Computing the price of an order

TaskCalculate the price of an orderTake into account if the customer has any discounts

Order

calculate pricecalculate base pricecalculate discounts

Productnameprice

Customernamediscount info

OrderLinequantity

*

1

1



Computation is concentrated in one class (centralisedcontrol)

The order computes the price by asking its collaborators aboutdata

→ centralised controlc©2011 H. Baumeister (IMM) Software Engineering I (02161) Spring 2011 48 / 65


Centralised Control: Class diagram

Order


Productnameprice

Customernamediscount info

OrderLinequantity

*

1

1

Only class Order has any interesting behaviourOrderLine, Customer, and Product are purely data classes (nomethods)



Computation is distributed among several objects(distributed control)

The order computes the price by delegating part of the pricecalculation to order line and customer

→ distributed controlc©2011 H. Baumeister (IMM) Software Engineering I (02161) Spring 2011 50 / 65


Distributed Control: Class diagram

Order


Productnamepriceget price for quantity

Customernamediscount infocalculate discount

OrderLinequantitycalculate price

*

1

1

More customer types can beaddedEach computing the discountdifferently

The product nowcalculates the pricedepending on quantityOne could now haveproducts that arecheaper the more onebuys



Design for change (I): Centralized Control

centralized control

B CA

m 0m1(B)m2(C)m3(D)

D

public class A {private B b;private D d;public void m0() {

m1(b);C c = getC();m2(c);m3(d);

}public void m1() {...}public void m2() {...}public void m3() {...}

}

Question: How easily can m0 be

adapted?



Design for change (II): Distributed Control

distributed control

A

m 0

B

m1(A)m2(A)

D

m3(A)

C

m2(B)

public class A {private B b;private D d;public void m0() {

b.m1(this);b.m2(this);d.m3(this);

}}public class B {

private C c;public void m2(A a) {

c.m2(this);}

}



Design for change (III): Distributed Control

distributed control

A

m 0

B

m1(A)m2(A)

D

m3(A)

C

m2(B)

B1

m1(A)m2(A)

D1

m3(A)

The behaviour of m0 can beadapted by using newsubclasses of A, B, C, and DThe subclasses have each theirown version of m0, m1, m2, andm3

What happens if a newsubclass, e.g. D2, is added?New subclasses can be easilyadded to adapt the behaviour,without m0 having to change

→ The system can be used andadapted to situations which onehas not thought of in thebeginning



Design for change (IV): Centralized Control

m0 has to deal itself with allpossible subclasses

→ use of instanceofWhat happens if a newsubclass, e.g. D2 is added tothe system?

→ m0 has to change



Centralised vs Distributed Control

Centralised controlOne method does all the workThe remaining objects are merely data objects and usually don’thave their own behaviourTypical for a procedural programming style

Distributed controlObjects collaborate to achieve one taskEach object in a collaboration has behaviour (= is a ”real” object)Typical object-oriented style

Each object has its own responsibilitiesCreates adaptable designs

Object-OrientationDistributed Control is a characteristic of object orientation


Summary

Summary

Activity DiagramsFrom requirements to design: CRC cardsSequence DiagramsObject Orientation: Centralized vs Decentralized control


Summary

Software Engineering I (02161)Week 5

Assoc. Prof. Hubert Baumeister

Informatics and Mathematical ModellingTechnical University of Denmark

Spring 2011


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