1
Lecture 5

• a bit more about UML
• Sequence diagrams
• Collaboration diagrams
• State-chart diagrams
• CRC cards

2
Misc

• Missing seminars for OOMPA E
• Monday 15/10 10-12 in Q32
• Wednesday 17/10 10-12 in V35
• Seminars
• It is mandatory to hand in your notes for the
  chapters you prepared for presentation after the
  seminar
• Labs
• Lab1 is due next Friday 28/9
• JAVA syntax highlighting in Emacs
• Press M-x and type font-lock-mode
• Add the line
• (require jde)
• to your .emacs file

3
System Model

• Scenarios
• - As-is scenarios, visionary scenarios
• Use case model
• - Actors and use cases
• Object model
• - Data dictionary
• - Class diagrams (classes, associations,
  attributes and behaviors)
• Dynamic model
• - State diagrams for classes with significant
  dynamic behavior
• - Sequence diagrams for collaborating objects
  (protocol)

4
Dynamic Modeling with UML

• Diagrams for dynamic modeling
• Interaction diagrams describe the dynamic
  behavior between objects
• Statecharts describe the dynamic behavior of a
  single object

5
Dynamic Modeling with UML

• Interaction diagrams
• Sequence Diagram
• Dynamic behavior of a set of objects arranged in
  time sequence, new objects added to the right
• Good for real-time specifications and complex
  scenarios
• Derived from use case scenario
• Collaboration Diagram
• Shows the relationship among objects. Does not
  show time
• Objects are arranged in a graph or network format

6
Sequence Diagrams vs Collaboration Diagrams

• Sequence diagram

ClassA
ClassB
message2()
message1()
message3()
7
Sequence Diagrams vs Collaboration Diagrams

• Collaboration diagram

message1()
ClassA
1. message2() ?
2. message3() ?
ClassB
8
Sequence Diagrams vs Collaboration Diagrams

• Sequence diagrams
• Strength clearly show sequence or time ordering
  of events, simple notation
• Weakness forced to extend to the right when
  adding new objects
• Collaboration diagrams
• Strength space economical flexibility to add new
  objects in two dimensions, better to illustrate
  complex branching, iteration and concurrent
  behavior
• Weakness difficult to see sequence of messages,
  more complex notation

9
Dynamic Modeling with UML

• State Chart Diagram
• A state machine that describes the response of an
  object of a given class to the receipt of outside
  stimuli (Events).
• Activity Diagram
• Special type of statechart where all states are
  action states

10
State Chart Diagram vs Sequence Diagram

• State chart diagrams help to identify
• Changes to objects over time
• Sequence diagrams help to identify
• The temporal relationship between objects over
  time
• Sequence of operations as a response to one ore
  more events

11
Dynamic Modeling

• Definition of dynamic model
• A collection of multiple state chart diagrams,
  one state chart diagram for each class with
  important dynamic behavior.
• Purpose
• Detect and supply methods for the object model
• How do we do this?
• Start with use case or scenario
• Model interaction between objects gt sequence
  diagram
• Model dynamic behavior of single objects gt
  statechart diagram

12
Start with Flow of Events from Use Case

• Flow of events from Process Sale Use case
• 1. Customer arrives at POS checkout with goods
  and/or services
• 2. Cashier starts new sale
• 3. Cashier enters item identifier
• 4. System records sale line item and presents
  item description, price and running total.
  Cashier repeats steps 3-4 until indicates done
• 5. System presents total with taxes calculated
• 6. Cashier tells customer the total and asks for
  payment
• 7. Customer pays and system handles payment

13
What is an Event?

• Something that happens at a point in time
• Relation of events to each other
• Causally related Before, after,
• Causally unrelated concurrent
• An event sends information from one object to
  another
• One distinguishes between
• The instance of an event enterItem
• The attributes of an event itemID, quantity

14
Sequence Diagrams

• From the flow of events in the use case or
  scenario proceed to the sequence diagram
• A sequence diagram is a graphical description of
  objects participating in a use case or scenario
  using a DAG (directed acyclic graph) notation
• Relation to object identification
• Objects/classes have already been identified
  during object modeling
• Objects are identified as a result of dynamic
  modeling
• Heuristic
• An event always has a sender and a receiver. Find
  them for each event gt These are the objects
  participating in the use case

15
Sequence Diagrams

• Use cases and participating objects are found.
  What now?
• Sequence diagram - A diagram that shows object
  interactions arranged in time sequence for a
  specific use case or scenario.
• A sequence diagram includes time but does not
  include object relationships.
• Sequence diagrams are used to describe use cases
  (i.e., all possible interactions between
  participating objects) and scenarios (i.e., one
  possible interaction)
• In other words A sequence diagram is useful to
  model a use case or scenario with its
  participating objects. It often leads to the
  detection of new participating objects.

16
Drawing Sequence Diagrams

• Each column represents an object that is
  participating in the interaction.
• The vertical axis represents time (from top to
  bottom). Messages are shown by full arrows.
• Labels on full arrows represent message names and
  arguments.
• Activations (i.e., the time it takes to perform
  an operation) are depicted by a rectangle
  attached to an object. The height of the
  rectangle is indicative for the duration of the
  operation
• The vertical rectangle shows that an object is
  active, that is, it is handling a request made by
  another object.
• The operation can itself send other requests to
  other objects
• An object can request an operation from itself
  (looping arrow)

17
Sequence Diagrams
Cashier
System
makenewSale()
enterItem(itemID, quantity)
description, total
endSale()
total
makePayment(amount)
change due, receipt
18
Sequence Diagrams

• Iterations
• may have square brackets containing a
  continuation condition (until) specifying the
  condition that must be satisfied in order to exit
  the iteration and continue with the sequence
• may have an asterisk followed by square brackets
  containing an iteration (while or for) expression
  specifying the number of iterations

19
Sequence Diagrams

• Iteration in sequence diagrams is denoted by a
  box with an associated iteration expression.

Cashier
System
makenewSale()
enterItem(itemID, quantity)
description, total
more items
20
Sequence Diagrams

• Iteration in sequence diagrams is denoted by a
  box with an associated continuation expression.

Cashier
System
makenewSale()
enterItem(itemID, quantity)
description, total
no more items
21
Sequence Diagrams

• Naming objects
• Class name only Classname
• Instance name only objectName
• Instance name and class name together
• objectClass
• Most of the time you use the class name, but if
  you refer to a particular instance in a scenario
  the objectClass notation is used.
• A scenario is an instance of a use case, where we
  take real or hypothetical people and things and
  follow them through the steps of the use case.

22
Sequence Diagrams

• Conditional messages A message might contain a
  guard condition denoted in square brackets

obj1Class
obj2 Class
message()
x lt 15 calculate()
23
Sequence Diagrams

• Sequence diagrams may contain branches. Branching
  involves multiple messages originating at the
  same time from a single class role.
• The branch represents conditionality if the guard
  conditions on all the branches are mutually
  exclusive. Thus, only one message is sent.
• The branch represents concurrency if the guard
  conditions are mutually inclusive. Thus multiple
  messages are sent.

24
Sequence Diagrams

• Conditionality

obj1Class
obj2 Class
obj3 Class
x lt 15 calculate()
message()
x gt 20 calculate()
25
Sequence Diagrams

• Concurrency

obj1Class
obj2 Class
obj3 Class
calculate()
message()
calculate()
26
Sequence Diagrams

• Creation and destruction of an object in sequence
  diagrams are denoted by the stereotypes
  ltltcreategtgt and ltltdestroygtgt

Creator
ltltcreategtgt
Created Object
message()
X
ltltdestroygtgt
27
Sequence Diagrams

• Iteration over a Collection (multiobject)
• The message is send to each element rather than
  repeatedly to the collection itself.

Sale
SalesLineItem
ttotal()
stsubtotal()
28
Collaboration Diagrams

• Collaboration diagrams contain
• Classes
• Associations
• Message exchanges within a collaboration
• Collaboration diagrams describe a set of classes
  and associations involved in message exchange
  sequences, that is a collaboration among class
  roles and association roles, and their
  interactions.

29
Collaboration Diagrams
makePayment(cash)
1 makePayment(cash)?
Register
Sale
1.1 create(cash) ?
Payment

• The first (external) message makePayment is sent
  to an
• instance of a Register. The sender is not
  identified.
• 2. The Register instance sends the makePayment
  message to
• to a Sale instance.
• 3. The Sale instance creates an instance of a
  Payment.

30
Collaboration Diagrams

• Link A link is a connection path between two
  objects, it indicates some form of navigation and
  visibility between the objects. A link is an
  instance of an association.
• Note that multiple messages, and messages both
  ways can be exchanged along the same link.

1 makePayment(cash)? 2 foo() ?
Register
Sale
2.1 bar() ?
link
31
Collaboration Diagrams

• Messages each message between objects is
  represented with a message expression and a small
  arrow indicating the direction of the message. A
  sequence number is added to show the sequential
  order of messages.

1 msg2()? 2 msg3() ? 3 msg4() ?
msg1()?
Register
Sale
3.1 msg5() ?
32
Collaboration Diagrams

• Creation of instances the stereotype ltltcreategtgt
  and the property new are used to indicate the
  creation of new instances.

ltltcreategtgt 1 make(cashier)?
Register
Sale new
33
Collaboration Diagrams

• Messages number sequencing The order of
  messages is illustrated with sequence numbers.
  The numbering scheme is
• The first message is not numbered
• The order and nesting of subsequent messages is
  shown with a legal numbering scheme, in which
  nested messages have a number appended to them.
  Nesting is denoted by prepending the incoming
  message number to the outgoing message number

msg1() ?
1 msg2()?
Register
Sale
1.1 msg3() ?
Payment
34
Collaboration Diagrams
msg1() ?
1 msg2()?
classA
classB
1.1 msg3() ? 2.1 msg5() ?
2 msg4()?
classC
2.2 msg6()?
classD
35
Collaboration Diagrams

• Conditional Messages A conditional message is
  shown by following a sequence number with a
  conditional clause in square brackets.

msg1()?
1 colorred msg2()?
Foo
Bar
36
Collaboration Diagrams
Mutually exclusive messages
1a test msg2()?
msg1() ?
classA
classB
1a.1 msg3() ?
1b not test msg4() ?
classC
classD
1b.1 msg5() ?
37
State Chart Diagrams

• The state of an object is defined by the set of
  values currently held by its attributes.
• At any moment in time, an object exists in a
  certain manner or conditon, which we say is a
  state.

Source State Entry and Exit actions
Target State
Event Guard / Action
38
State Chart Diagrams

• Statechart diagrams are useful when
• A class has an interesting or complex life cycle,
  e.g. classes that create or delete instances or
  associations
• An instance can update its attributes in a
  variety of ways as it goes through a life cycle.
• If two classes are depending on each other, in
  that one of them can start the other on its
  life-cycle, or change the order in which it goes
  from state to state.
• If you find that the objects current behavior
  depends on what happened to it before, that is on
  its past history.

39
Statechart Diagrams

• Graph whose nodes are states and whose directed
  arcs are transitions labeled by event names.
• Distinguish between two types of operations
• Activity Operation that takes time to complete
• associated with states
• Action Instantaneous operation
• associated with events
• associated with states (reduces drawing
  complexity) Entry, Exit, Internal Action
• A statechart diagram relates events and states
  for one class
• An object model with a set of objects has a
  set of state diagrams

40
Statechart Diagrams

• An action is an atomic behavior that is
  associated with a state or a transition, and is
  considered part of the life cycle.
• Atomic means that it cannot be split any further
  without losing or changing the meaning of what it
  was.
• An entry action is an action performed each time
  the object enters or reenters a state, regardless
  of how it got there.

41
Statechart Diagrams

• State diagram for book class showing entry and
  exit actions

Event B1 Subscriber requests loan
1 Shelved entry/ UpdateTimeShelved() exit /
UpdateTimeOut()
Event B3 Librarian shelves book
3 Checked entry/ Loan.L2 Archive Loan
2 Signed Out entry/ Loan.L1 Request Link to
Subscriber exit / UpdateTimen()
Event B2 Subscriber returns book
42
Statechart Diagrams

• The life-cycle of a loan instance

ltltcreategtgt Event L1 Request Link to subscriber
(Book ID No., Subscriber ID No., Date/Time Out)
1 Current
Event L2 Archive Loan (Date/Time In)
initial state
2 Archived entry/ UpdateTimeIn()
Event L3 After (90 days) /delete archived loan
final state
43
CRC cards

• Class-Responsibility-Collaborators (CRC) cards
  are a useful tool to assign responsibilities to
  classes
• Not part of UML
• Use 10x15 cm index cards
• Use one card for each class
• A CRC card contains
• Class name
• Responsibilities
• Collaborations

44
CRC cards

• Class name

Responsibilities
Collaborators
45
CRC cards

• CRC modeling is carried out by a team of people
• The goal of CRC modeling is
• to identify the classes that are appropriate for
  modeling the problem (similar to domain class
  model)
• To identify their responsibilities and
  collaborations

46
Finding Responsibilities

• Responsibilities
• Things a class needs to know about (attributes) a
  class Person will know things like
• name, address, phone number
• Things a class needs to be able to do (methods),
  a class Addressbook needs to be able to
• add/remove a person to an addressbook
• Look up a person in the adressbook
• Sort the the adressbook in alphabetical order

47
Finding Collaborators

• For each responsibility we must ask
• Does the class have everything it needs to do
  this? Does it have all the attributes?
• What classes are there that can supply this
  information? If so record these classes as
  collaborators. There might be a chain of
  collaborators.
• If some of the things needed are not available
  from any class at all
• Add an attribute to an existing class
• Define a new class

48
Observer Pattern

• Observer
• Responsibilities
• Subscribes to subjects it is interested in.
• Implements a strategy to respond to changes of
  the subjects it subscribed to
• Collaborators
• Subject

49
Observer Pattern

• Subject
• Responsibilities
• Maintains and provides information about itself.
• Notifies observers about changes of its state as
  information is updated
• Collaborators
• Observer