UML and the Software Development Process

1
UML and the Software Development Process

• expanding the design process
• UML Use Cases
• UML class diagrams

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Software Development

• a software development process (or method or
  methodology) specifies who is doing what when,
  and how to transform the stakeholders'
  requirements into a software system
• the key to communication between people involved
  in the process is a modeling language usually a
  graphical notation for expressing e.g. class
  designs
• we use UML, the Unified Modeling Language "A
  graphical language for visualising, specifying,
  constructing and documenting the artifacts of a
  software-intensive system"
• UML has 9 types of diagram, but we will look at
  only 3
• we have been using these informally in lectures

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Analysis Design Implementation

• Analysis
• establish the rationale, scope and purpose
• build a model of the problem domain (not the
  software)
• use case diagrams, class diagrams, sequence
  diagrams
• Design
• decide on the software classes and interfaces
• class diagrams, sequence diagrams and GUI
  mock-ups
• Implementation
• write code for each class, carry out testing
• class diagrams, sequence diagrams

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Analysis problem domain class identification

• "underline the nouns in your requirements
  documentation"
• good in theory, but in practice ...?
• problem domain classes will be revealed
• in discussion with domain experts (recurring
  terms, terms they define, ...)
• by seeing physical manifestations (real order
  forms,...)
• from existing software systems
• from refining your diagrams (e.g. new classes
  sometimes arise from what you initially thought
  were relationships)

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Analysis scenarios

• a scenario is one thing that can happen when
  running the software
• Example 2 scenarios for an online CD store
• the user logs on to the system, browses a list of
  CDs, spots the one she wants, adds it to basket,
  proceeds to "checkout", enters her credit card
  details, confirms the purchase, system checks
  authorisation, confirms the sale, queues CD for
  packing and dispatch
• the user logs on to the system, ..., enters
  credit card details, confirms the purchase,
  authorisation fails, user exits the system

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Analysis Use case

• a use case is a set of scenarios tied together by
  a common user goal
• Example "buy a CD" use case consists of the two
  previous scenarios (success, fail credit card)
  plus others
• Typically, a use case will have one "as expected"
  scenario, plus a number of related scenarios for
  failures or alternative paths to success
• You must decide which scenarios fit into a use
  case, and which require new use cases

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Analysis Use Case text description

• Buy a CD
• Main Success Scenario
• Customer logs on
• Customer browses list
• Customer selects CD
• Customer proceeds to checkout
• Customer enters credit card details
• Credit company authorises
• Dispatcher queues for delivery

Extensions 3a Customer quits 6a credit
refused 6a1 customer may re-enter or quit
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Analysis Use Case Diagrams
stock controller
system engineer
authorisation
credit company
customer
dispatcher
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Analysis using Use Cases

• the Use Case diagram is a formal part of UML
• an actor is a role a user plays with respect to
  the system
• one human user can be multiple actors
• actors can be external systems
• identifying the actors helps decide on the use
  cases
• one use case can include another
• one use case can generalise another
• Use cases are extremely useful in analysis, and
  help to guide the design phase
• the text descriptions are informal
• you can include many different types of
  requirement
• the text is more useful than the diagram

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Design

• draw a class diagram showing software classes
• "problem domain" classes may have corresponding
  software classes
• boundary classes mediate between the software and
  its clients
• control classes coordinate workflow between
  objects
• interfaces hide classes in which change is
  anticipated
• include navigability arrows on associations
• draw sequence diagrams
• draw GUI mock-ups

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Software class identification

• a software class is an abstraction around data
• state (attributes/instance variables) and
  behaviour (operations/instance methods)
• identify candidate classes from design patterns,
  code libraries (reuse!), data structures
  textbooks and courses, experience, discussion
  with others, etc
• candidate classes that are not abstractions of
  data should arouse suspicion (unless they are
  control classes)
• classes with names that are processes
• classes with no attributes or no methods

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Class diagrams

• a class diagram shows classes and their
  relationships
• association a customer may have a purchase
  history
• subtypes a DVD is a type of product
• they model parts of the structure of your problem
  domain or software system
• you don't have to show all attributes or
  operations concentrate on the important ones
  that help understanding
• can specify type, visibility, parameters and
  return type

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Class diagram examples
CD getTitle getName match
CD title name getTitle getName match
CD
CD -title String -name
String getTitle()String getName()String match
(String)boolean
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Class diagrams Association

• Association objects of class A are connected to
  objects of class B
• shown by a solid line between the classes
• may have a name
• open arrow indicates navigability (A -gt B means A
  "knows" it links to B, but B doesn't know about
  A)
• can also show multiplicity ( Am -gt nB means A
  links to n Bs, and B links to m As)
• i..j means links to between i and j items
• means links to any number of items

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Class Diagrams Generalisation

• Generalisation every B is a special kind of A
• shown by a solid line with a closed white arrow,
  pointing from subtype to parent type
• use italics for abstract classes and abstract
  methods
• also able to show the implements relationship
• shown by a dashed line with a closed white arrow
• interfaces are shown as a circle, or like a
  class, but with "ltltinterfacegtgt" before the class
  name

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Class diagram online store specification
1
1
1
1
Store
Customer
StoreGUI
1
1

BasketItem


1
Item
CD
DVD
Book
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Alternative store specification
1
1
1
1
Store
Customer
StoreGUI
1
1
1
1
1
1
Catalogue
Basket
History
1
1
1



1
BasketItem
Item

CD
DVD
Book
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detailed specification
1
1
1
1
Customer -id int -basket
ArrayListltBasketItemgt -history
ArrayListltBasketItemgt Customer(int) getId()
int getBasket() ListltBasketItemgt getHistory()
ListltBasketItemgt readFromFile(Store)
void saveToFile() void toString() String
StoreUDGui -customer
Customer -store Store -ud UserDialog StoreUDGui
(Store) displayBasketItems(ListltBasketItemgt,
String)
void displayCatalogueItems(ListltCatalogueItemgt,
String)
void findInCatalogue(ListltCatalogueItemgt,
int) CatalogueItem findInB
asket(ListltBasketItemgt
int) BasketItem addItemToBasket()
void changeItemDetails() void removeItemFromBas
ket() void searchCatalogue()
void searchBasketItems(ListltBasketItemgt)void pu
rchaseBasket() void interactWithUser() void
Store -catalogue
ArrayListltCatalogueItemgt -customer
Customer -nextId int Store() loginCustomer(Cust
omer) boolean logoutCustomer()
void getNextIdWithoutIncrementing()
int getNextId() int getCatalogue()
ListltCatalogueItemgt getCustomer()
Customer getItem(int) CatalogueItem -readCatalog
ueFromFile() void -readNextUserIDFromFile()
void toString() String
1
1



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BasketItem -itemCatalogueItem -n
umber int BasketItem(CatalogueItem,int) setNumb
er(int)void getItem() CatalogueItem getNumber(
) int saveToFile(PrintWriter) toString()
String matches(String) boolean
CatalogueItem -title
String -number int -price double CatalogueItem(
String,int,double) getTitle()
String getNumber() int getPrice()
double toString() String matches(String)boolea
n
Book -author
String -publisher String -isbn
String Book(String,int,double,String,String,Strin
g) getAuthor() String getPublisher()
String getIsbn() String readFromFile(BufferedRe
ader) Book
CD -artiste
String -recordLabel String CD(String,int,double,
String,String) getArtiste() String getRecordLab
el() String readFromFile(BufferedReader) CD
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detailed specification (fragment)


1

BasketItem -itemCatalogueItem -n
umber int BasketItem(CatalogueItem,int) setNumb
er(int)void getItem() CatalogueItem getNumber(
) int saveToFile(PrintWriter) toString()
String matches(String) boolean
CatalogueItem -title
String -number int -price double CatalogueItem(
String,int,double) getTitle()
String getNumber() int getPrice()
double toString() String matches(String)boolea
n
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Next lecture ...

• UML for specifying control flow