Side 1

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Introduction to UML

• Carsten Helgesen
• Department of Computer Engineering
• Bergen University College
• Bergen, Norway

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Outline

• Object oriented concepts.
• Unified Modelling Language - UML
• History.
• The various UML diagrams.
• Using UML in a development process.
• From model to implementation - Mapping to Java.

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The object oriented approach
Object Identity Behaviour State
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Classes Java-like example

• class Person attributes name String
• address String
• birthDate Date
• methods print() age() Integer

• class Car attributes make
  String registrationNr String speed
  Integer owner Personmethods start() stop(
  ) drive(speed Integer)

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Classes An interpretation
What are you?
What do you know?
Concept
What can you do?
Who do you know?
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Some object oriented concepts

• Objects, classes.
• Attributes.
• Operations.
• Associations.
• Generalisation, inheritance.
• Message passing.

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Message passing

• Procedural paradigm Operations are performed by
  calling functions.
• E.g. printPage(Book, 1), print(book).
• Object oriented paradigm Perform operation
  passing messages to object. A class has a method
  to perform the requested action when receiving a
  message.
• An object knows how to perform its methods on
  itself.
• Common notation Result Object.Message.
• Message is passed to Object, which responds by
  returning Result.

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Java example

• Class Library
• printFirstPage(isbn String)
• Book aBook
• Page aPage
• aBook getBook(isbn)
• aPage aBook.page(1)
• aPage.print()

Message to itself
Message to aBook
Message to aPage
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What is UML?

• UML Unified Modelling Language.
• Notation for visual object oriented modelling of
  systems
• Not necessarily software systems!
• Visual 'blueprint' of system.
• Medium for communication between people
• Domain experts (users) and software developers.
• Development team.
• Usable in all stages of software development
• Use same diagram types for different purposes.
• Allow increase level of detail during development.

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UML history

• Until 1994 Many different competing methods for
  object oriented modelling and system development.
  The methods had different notations, different
  focus and different but similar concepts. gt
  Confusion, methods war.
• 1994 Grady Booch and James Rumbaugh (Rational
  Software Corporation) started developing a
  Unified Method to unite their methods Booch and
  OMT.
• 1995 Ivar Jacobson joined Rational, adding
  elements from his method OOSE - in particular
  Use-Case.
• 1997 Version 1.0 of UML approved for
  standardisation by Object Management Group (OMG).

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UML information sources

• Books
• http//www.amazon.com/ - search with keyword
  UML
• M. Fowler UML Distilled, Addison-Wesley,
  2002- Short introduction to UML - excellent
• C. Larman Applying UML and patterns,
  Prentice-Hall 1998- Explaining UML through an
  iterative development process.
• http//www.cetus-links.org

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UML diagrams

• Use-case diagram
• Class diagram
• Package diagram
• Sequence diagram
• Collaboration diagram
• State diagram
• Activity diagram
• Component diagram
• Deployment diagram

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Use-case diagram

• A use-case diagram captures user requirements.
• Focus on what a system should do, seen from the
  outside.
• Model elements
• Actor Someone or something interacting with the
  system.
• Use-case A complete functionality, as seen from
  an actor.
• Actors model external environment, use-cases
  model internal actions and responsibilities.

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Use-case description

• A use-case must be described in text.
• Purpose Understand and document the use-case.
• Example
• Use-case Buy goods
• Actors Customer, Cashier
• Type Primary
• Description A Customer arrives at a checkout
  with items to purchase. The Cashier records
  the items and presents the sum. The Customer
  pays the bill, takes the goods and leaves the
  shop.

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More detailed use-case description

• use-case Buy goods
• Actors Customer, Cashier
• Type Primary
• Description
• Actor action System response
• 1. A Customer arrives with items.
• 2. The Cashier records each item.
• 3. Determine the item price and add the
  item information to the transaction.
• 4. When all items are recorded, the Cashier
  indicates finished.
• 5. Calculate and present the sale total.
• 6. The Customer pays the bill.
• 7. Register payment, and print receipt.
• If cash see section Cash Payment
  If card see section Card Payment
• If cheque ...
• 8. The Customer leaves with items.

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Sequence diagrams

• A sequence diagram illustrates how objects
  interact by passing messages.
• Focus on time aspects of interaction.
• Model elements
• Objects represent actors, whole system or class
  instances.
• Messages sent between objects.
• Guards define conditions for messages to be
  sent.
• Lifeline shows explicit order of messages over
  time.
• Activation shows how long an object is active.
• Transition instance showing the time a message is
  sent.
• Transition time constraining how long a
  transition can take.

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Sequence diagram, example 1
Time
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Sequence diagram, example 2
System
Guard
Message
Activation
Return
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Class diagram

• A class diagram models
• Concepts (things) and relationships in the
  application domain
• Classes in the implementation , e.g Java classes
• Model elements
• Object, Class
• Attribute
• Operation (Method)
• Association, aggregation
• Generalisation
• Constraint
• Package

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Class diagram domain model
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Generalisation (1)

• Generalisation - one class (the sub-class) is a
  more specific variant of another class (the
  super-class).
• Expresses the is-a-kind-of relationship
• E.g. Cheque is-a-kind-of Payment

Generalisation relationship
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Generalisation (2)
Multiple classification
incomplete, overlapping
complete, disjoint
sex
occupation
Multiple inheritance
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Generalisation in a Venn diagram

• A Venn diagram can illustrate sub- and
  superclasses

A
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Example model
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Packages

• Package - organising elements into useful groups.
• Each class belongs to exactly one package.
• Can use a class from another package
• Dependency between packages - a package uses
  classes from another package
• Useful for managing complexity, organising the
  model into smaller parts, possibly
  hierarchically
• Packages contain classes.
• Packages contain packages.

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Package (1)
Package
Classes in the package
Dependency
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Package (2)
Shops
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Package (3)
Class imported from package Shops
Products
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Package (4)
Sales
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State diagrams

• A state diagram describes the state of an object,
  and change of state due to received stimuli.
• Focus on life cycle of an object.
• Model elements
• State representing a situation during the life of
  an object.
• State variables
• Internal state activities
• Transition representing a change from one state
  to another
• Event specifying events leading to a transition
• Guard specifying a condition for when a
  transition can happen
• Action specifying actions involved in a
  transition
• UML syntax Event Guard / Action

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State diagram (1) Buy Goods

• State diagram for till in use-case Buy Goods

Event
Action
Start state
State
Transition
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State diagram (2) Buy Goods

• Detailed state diagram for till in use-case Buy
  Goods

Event
Guard
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State diagram (3) Digital watch
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Activity diagrams

• An activity diagram describes the activities
  involved in an operation or a use-case. Variant
  of a state diagram.
• Focus on the work that is performed.
• Model elements
• Activity is a task is part of the activity.
• Decision point is where a choice is made.
• Transition defines the sequence of activities.
• Guard describes a condition for when a transition
  can happen.
• Concurrency bar defines concurrent activities
• Split bar indicates activities that can happen
  concurrently.
• Unite bar indicates co-ordination of concurrent
  activities.
• Swim lanes assigning responsibility for
  performing activities.

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Activity diagram (1)

• Based on figure 9-2 from UML Distilled.

Reorder Item
Iteration
not in stock
Unite bar (Synchronise)
Outstanding Order
Decision
Check OrderItem

Assign to Order
in stock
Receive Order
Dispatch Order
Authorise Payment
succeed
Split bar (Parallel)
Transition
failed
Cancel Order
Guard
Activity
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Activity diagram with swim lanes

• Based on figure 9-5 from UML Distilled.

Reorder Item
not in stock
Order Processing
Decision
Outstanding Order
Swim lanes
in stock

Check OrderItem
Assign to Order
Dispatch Order
Receive Order
Cancel Order
succeed
Authorise Payment
Finance
failed
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Component diagrams

• A component diagram describes software components
  and their dependencies to each other.
• Focus on assigning logical functionality to
  software components.
• Model elements
• Components represent software components.
• Types of components, e.g.
• Compile time Source, binary, executable.
• Runtime Executable, DLL.
• Web html, applet, documentation, image.
• Dependencies show how one component uses other
  components.
• One component using classes from another
  component.
• Compilation dependencies.

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Component diagram 1
Component
Component type
Dependency
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Component diagram (2)
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Deployment diagrams

• A deployment diagram shows the run-time
  architecture of processing elements and objects
  living on them.
• Focus on physical architecture.
• Model elements
• Nodes representing computational (hardware)
  resources.
• Can be either type (class) or instance (object).
• E.g. processors, printers, routers.
• Connections between nodes.
• E.g. TCP/IP, DecNet.
• Components representing software running on a
  node.

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Deployment diagram
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Development process (1)

• UML is a modelling language, not a process. But
  it should be used within some process framework.
• A development process defines
• what to do (tasks),
• how to do it (tools),
• when to do it (task order),
• why it should be done (motivation),
• what should be the result (products).

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Development process (2)
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Requirements

• Focus
• View system from outside / user point of view.
• Domain (business) data and processes.
• Non-technological.
• Activities
• Discussions with customer.
• Understand requirements of system.
• Products
• Business terms (dictionary).
• Business processes.
• UML diagrams Use-case / simple class / simple
  activity.

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Analysis

• Focus
• Domain data (business) and processes.
• Non-technological.
• Activities
• Discussions with customers / users.
• Understand problem domain data and processes in
  detail.
• Describe terms / classes / association /
  behaviour in detail.
• Products
• Detailed but ideal conceptual model.
• UML diagrams Use case / class / sequence / state
  / activity

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Design

• Focus
• Implementing system on a computer.
• Technological.
• Activities
• Divide into functional packages / layers
  (architecture).
• Extend analysis model with implementation
  details
• user interface, storage, communication, methods
  etc.
• Products
• System architecture.
• UML diagrams Class / behaviour / component /
  deployment.

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Implementation

• Focus
• Programming.
• Activities
• Write program code based on system design.
• Products
• Programs.
• Program documentation.
• UML diagrams Class / package / component /
  deployment

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Discovering the model - CRC cards

• CRC cards is a simple method for
• learning object oriented thinking,
• identifying an object oriented model of an
  application domain.
• CRC Class, Responsibility, Collaboration
• Developed in late 80s by K. Beck and W.
  Cunningham.
• Uses index cards to capture...
• a class,
• its responsibilities - what the class knows and
  does,
• classes it needs to contact to perform its
  responsibilities - collaborations
• Encourages small classes with few
  responsibilities.

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CRC cards Example
Class
Sale
Responsibility
Record items
Sale Item
Find total amount
Sale Item
Register payment
Payment
Sales Item
Date
Record product
Product
Description
Product Spec.
Quantity
Collaborations
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Mapping to Java Example (1)
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Mapping to Java Example (2)

• public class Sale / Attributes /private
  Boolean isCompletepublic Date date/ Methods
  /public Boolean makeComplete()public void
  makePayment()public Double total()/
  Associations /public SalesItemVector
  itemspublic Payment thePayment

• public class SalesItempublic Integer
  quantitypublic Product theProductpublic
  ProductSpec description
• public class Payment public Double amount
• public class Cash extends Payment

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Code generation from UML

• UML can be mapped automatically to a programming
  language implementing the modelled structures.
• CASE tools can generate code from an UML model.
  Mapping can be into
• Programming languages C, Java, ...
• Visual programming toolsVisual Basic, Delphi,
  ...
• RDBMS Oracle8, SQL DDL, ...
• OODBMS O2, ObjectStore, Objectivity, POET, ...
• Middle ware Persistence, Rogue Wave, Corba IDL,
  ...

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Reverse Engineering to UML

• In many cases an implementation can be reverse
  engineered into a UML model.
• Round Trip Engineering
• Rational Rose can reverse engineer from several
  sources
• Programming language Java, C
• RDBMS Oracle8

UML modelling
Reverse Engineering Java to UML
Mapping UML to Java
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Summary

• We have discussed most of UMLs modelling
  elements
• User requirements
• Use-case diagram, activity diagram.
• Static aspects
• Class diagram, Package diagram.
• Dynamic aspects
• Sequence diagram, Activity diagram, State
  diagram.
• Mapping to implementation platform
• Relational database.
• OO programming language, e.g. Java.

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How to make good UML models

• Practice!
• Practice!!
• Practice!!!
• Stick to the KISS principle
• Keep It Simple, Stupid!

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UML is not a silver bullet

• Usual mode of software development is still
  often...