08 class and sequence diagrams

INTROSE Introduction to Software Engineering

Raymund Sison, PhDCollege of Computer Studies

De La Salle University

[email protected]

Modeling Software Systems

How do we model complex systems?Epistemology

Knowledge about Causality

(Dynamic Model)

Describes our knowledge about the system

Knowledge about Functionality(Functional model)

Knowledge about Relationships(Object model)

Neural Networks

DataFlow Diagrams (SA/SD)

Scenarios/Use Cases(Jacobsen)

Formal Specifications

(Liskov)

Petri Nets(Petri)Inheritance

Frames,SemanticNetworks (Minsky)

Uncertain KnowledgeFuzzy Sets (Zadeh)

Data Relationship(E/R Modeling, Chen)

Hierarchical Database

Model (IMS)

NetworkDatabase

Model(CODASYL)

RelationalDatabase Model

(Codd)

Fuzzy Frames(Graham)

Class Diagrams(“E/R + Inheritance”,

Rumbaugh)

Sequence Diagrams(Lamport)Activity

Diagrams(“good old Flowcharts”)

From (Bruegge & Dutoit, 2004)

How do we model complex systems?

Epistemology


(Dynamic Model)




Neural Networks




(Liskov)






Model (IMS)

NetworkDatabase

Model(CODASYL)


(Codd)



Rumbaugh)




Components of an Object Model

ClassesAssociations (Relations) Kind-of/Is-a (Generalization) Part-of/Has-a (Aggregation) Domain-specific associations

AttributesOperations

UML Classes

A class is simply represented as a box with the name of the class inside

The diagram may also show the attributes and operations

The complete signature of an operation is: operationName(parameterName: parameterType …): returnType

Class Diagram slides from (Lethbridge & Laganiere, 2005)

Associations and Multiplicity

An association is used to show how two classes are related to each other

Symbols indicating multiplicity are shown at each end of the association

Labelling Associations

Each association can be labelled, to make explicit the nature of the association

Analyzing and Validating Associations

Many-to-one• A company has many employees,

• An employee can only work for one company. This company will not store data about the moonlighting

activities of employees!

• A company can have zero employees E.g. a ‘shell’ company

• It is not possible to be an employee unless you work for a company

*worksForEmployee Company1


Many-to-many• An assistant can work for many managers

• A manager can have many assistants

• Assistants can work in pools

• Managers can have a group of assistants

• Some managers might have zero assistants.

• Is it possible for an assistant to have, perhaps temporarily, zero managers?

*

supervisor

*****1..*Assistant Manager


One-to-one• For each company, there is exactly one board of

directors

• A board is the board of only one company

• A company must always have a board

• A board must always be of some company

Company BoardOfDirectors11


Avoid unnecessary one-to-one associations

Avoid this Do this

A More Complex Example

A booking is always for exactly one passenger • no booking with zero passengers

• a booking could never involve more than one passenger.

A Passenger can have any number of Bookings• a passenger could have no bookings at all

• a passenger could have more than one booking

The frame around this diagram is an optional feature that any UML 2.0 may possess.

Association Classes

Sometimes, an attribute that concerns two associated classes cannot be placed in either of the classes

The following are equivalent

Reflexive Associations

It is possible for an association to connect a class to itself

Directionality in Associations

Associations are by default bi-directional It is possible to limit the direction of an

association by adding an arrow at one end

Generalization

Specializing a superclass into two or more subclasses

A generalization set is a labeled group of generalizations with a common superclass

The label (sometimes called the discriminator) describes the criteria used in the specialization

Avoiding Unnecessary Generalizations

Inappropriate hierarchy ofclasses, which should beinstances

Avoiding Unnecessary Generalizations

Improved class diagram, with its corresponding instance diagram

Handling Multiple Discriminators

Creating higher-level generalization

Handling Multiple Discriminators

Using multiple inheritance

Object Diagrams

A link is an instance of an association (in the same way that we say an object is an instance of a class)

Associations vs. Generalizations in Object Diagrams

Associations describe the relationships that will exist between instances at run time. • When you show an instance diagram generated

from a class diagram, there will be an instance of both classes joined by an association

Generalizations describe relationships between classes in class diagrams. • They do not appear in instance diagrams at all.

• An instance of any class should also be considered to be an instance of each of that class’s superclasses

Aggregation

Aggregations are special associations that represent ‘part-whole’ relationships.

The ‘whole’ side is often called the assembly or the aggregate

This symbol is a shorthand notation association named isPartOf

When to Use an Aggregation

As a general rule, you can mark an association as an aggregation if the following are true: You can state that

• the parts ‘are part of’ the aggregate

• or the aggregate ‘is composed of’ the parts

When something owns or controls the aggregate, then they also own or control the parts

Composition

A composition is a strong kind of aggregation If the aggregate is destroyed, then the parts are

destroyed as well

Two alternatives for addresses

Aggregation Hierarchy

Propagation

A mechanism where an operation in an aggregate is implemented by having the aggregate perform that operation on its parts

At the same time, properties of the parts are often propagated back to the aggregate

Propagation is to aggregation as inheritance is to generalization. • The major difference is:

inheritance is an implicit mechanism propagation has to be programmed when required

Interfaces

An interface describes a portion of the visible behavior of a set of objects.

An interface is similar to a class, except it lacks instance variables and implemented methods

Notes and Descriptive Text

Descriptive text and other diagrams• Embed your diagrams in a larger document

• Text can explain aspects of the system using any notation you like

• Highlight and expand on important features, and give rationale

Notes: • A note is a small block of text embedded in a UML

diagram

• It acts like a comment in a programming language

How do we model complex systems?Epistemology


(Dynamic Model)




Neural Networks




(Liskov)






Model (IMS)

NetworkDatabase

Model(CODASYL)


(Codd)



Rumbaugh)




UML Interaction Diagrams

Model the dynamic aspects of the system by showing relationships among objects and the messages they may dispatch

Capture the behavior of a single use case Show a number of example objects and the

messages that are passed between these objects within the use case

UML Interaction Diagrams

Sequence Diagram Emphasizes the time ordering of messages Focuses on the chronological course of the

messages

Collaboration Diagram Emphasizes the organization of the objects

that participate in an interaction Focuses on the cooperation among objects

UML Collaboration Diagram

Shows a set of interactions between selected objects in a specific, limited situation, focusing on the relations between the objects and their topology

The chronological course of communication with each other is marked by numbering the messages

Shows the chronological sequences of the messages, their names and responses, and their possible arguments

One collaboration diagram for each use case

Link

Links between objects are like associations in the class model

Enables objects to send messages There should be an association in the class

model between the two link objects Links may be instances of associations that are

shown in the class diagram

Message

Links may be labeled with the names of messages

A communication between two objects that conveys information with the expectation that action will ensue

An event sent from one object to another An operation being invoked on another object Creation or destruction of an object instance

Collaboration Diagram

Show objects and links

Superimpose messages on links

a : Assembly

part : CatalogEntry

1.1: number = getNumber(): Client

1 : count(part)

Collaboration Diagram

: Registrar

course_form : CourseForm

theManager : CurriculumManageraCourse : Course

4 : <<create>>

3 : add_course()

1 : set_course_info()2 : process_form()

Message Sequence

Sequence of messages are determined by numbering

Defines the order in which the interaction takes place 1, 2, 3, 4, ….. 1, 1.1, 1.2, 1.3, 2, 2.1, 2.1.1, 2.2, 3

(shows which operation calls which other operation)

Sequence Diagram

Used to show the same interaction in a collaboration diagram but emphasize the order of the messages over time• Object instances are arranged horizontally

across the page

• Time runs vertically down the page

• Messages flow from left to right or from right to left

Sequence Diagram

Time

Objects and Message Flows

Lifeline

Objects are displayed at the top of the diagramThe vertical dimension represents timeEach object has a dashed line – lifeline – extending below it – to indicate the period of time during which objects playing that role actually exist

Object Name

Message

The messages in an interaction are drawn from top to bottom, in the order that they are sent.

Messages are shown as arrows pointing from the lifeline of the role sending the message to the lifeline of the receiver.

When a message is sent, control passes from the sender of the message to the receiver.

Object Name Object Name

message

Return

Return of control is shown using dashed arrow returning to the calling object.

Object Name Object Name

message

Activation

• Period of time during which an object is processing a message

• Shown on a lifeline as a narrow rectangle whose top is connected to a message

• When an object finishes processing a message, control returns to the sender of the message

Sequence Diagram

a : Assembly

part : CatalogEntry

getNumber()

: Client

count(part)

return number

Lifeline

Activation(optional)

Messages

control returns to the sender of the message (optional)

Hierarchical Numbering of Messages

1.11

1.2

22.1

2.22.2.1

2.1.1

2.1.2

Object Creation

course_form :CourseForm

theManager :CurriculumManager

aCourse :Course

: Registrar

set_course_info

process_formadd_course

<<create>>

Objectcreation

Object Creation: Order Entry Example

Order OrderLinequantity: integer

cost: float

CatalogEntry

1 * 1*

: Client: Order :

CatalogEntry

OrderLine(qty,part)add(qty,part)

: OrderLinegetCost()

return cost

Objectcreation

Object Destruction: Order Entry Example

: Client: Order

<<destroy>>remove(line)

: OrderLine

Objectdeletion

X

Recurrence

When a sequence of messages takes place within an iteration, messages are grouped together within a rectangle

Object Name Object Name Object Name

message

message

*[recurrence condition]

Branching

• Shown by 2 arrows branching off from the same point• Condition-clause is added to the message to show the condition

Object Name Object Name Object Name

[condition]message

[condition]message

Conditional Message

• Messages which are sent only under certain circumstances• Not used in most cases because of the complexity of the resulting diagrams• Consists of a Boolean expression written in square brackets

Conditional Message: Sequence Diagram

: Client: Order :

CatalogEntry

[s>=qty] OrderLine(qty,part)

add(qty,part)

: OrderLine

getCost()

return cost

getStockLevel(part)

return s

Conditional Message: Communication Diagram

: Order : OrderLine

{new}

: CatalogEntry

1: add(qty, part)

1.2: [s>=qty] OrderLine(qty, part)

1.2.1: cost = getCost()

{new}

: Client

{new}

1.1: s =

getStockLevel(part)

Message to Self

• A message that an object sends to itself gives rise to a new activation

• The new activation takes place in an object that already has a live activation

• The recursive nature of this new activation is shown by superimposing the new activation on top of the original one

Self-Delegation: Sequence Diagram

: Client: Order : Customer

getShippingCost()

getTotal()

: OrderLine *

getLocation()

*getValue()

Self-Delegation: Collaboration Diagram

: Order : Customer

: OrderLine *

1: getTotal()

1.2.1: getLocation()

: Client1.1*: g

etValue()

1.2: getShippingCost()

<<self>>

08 class and sequence diagrams

Technology

associations associations

object diagrams associations

associations onetoone

relationships object

reflexive associations

labelling associations

association classes

association generalizations