Topics for Week 7

1
Building an Analysis Model of the System Under
Development
2
Developing your design from the product
specifications Remember there is probably not a
UNIQUE GOOD DESIGN for a given set of
specifications But there are many BAD
designs The goal of the design stage is to come
up with a good design and to avoid bad design
choices We will use some of the UML tools to
explore the design and test out our design
choices with respect to the specifications we are
given, before we invest time and energy in actual
coding.
3

• Question How do you start an OO design?
• --components?
• --objects?
• --how will they interact?
• Answer One common method is to start with
  components, along with any design patterns which
  can be identified.
• In general
• design is an iterative process
• all team members should take an active part in
  exploring possible designs
• simple designs are preferable to complex
  designs--but it may take several iterations to
  develop a simple design which meets the project
  requirements
• As explained previously, we will use a subset of
  UML to do the project design.

4
Analysis model (UML version) --functional model
(use cases and scenarios) --analysis object
model (static class and object
diagrams) --dynamic model (state and sequence
diagrams) As system is analyzed, specifications
are refined and made more explicit if necessary,
requirements are also updated
5
Figure 5-19 of text an activity diagram for
analyzing the system you are building
6
Review use case Graphical description
Text description Use case
name Participating actors Flow of events Entry
condition(s) Exit condition(s) Quality
requirements
Homeowner
Accesses system via internet
Sensors
System administrator
Reconfigures sensors and related system
features
Pressman, p. 163, Figure 7.3
7
Class and object diagrams Identify Objects from
Use Case Specifications USE ENDUSERs TERMS AS
MUCH AS POSSIBLE Entity objects things, for
example --nouns (customer, hospital,
infection) --real-world entities (resource,
dispatcher) --real-world activities to be tracked
(evacuation_plan) --data sources or sinks
(printer) Boundary objects system interfaces,
for example --controls (report(emergencybutton) -
-forms (savings_deposit_form) --messages
(notify_of_error) Control objects usually one
per use case --coordinate boundary and entity
objects in the use case Use the identified
objects in a sequence diagram to carry out the
use case
8
Common classes

• Other common types of classes which the developer
  can look for include
• tangible things, e.g., Mailbox, Document
• system interfaces and devices, e.g.,
  DisplayWindow, Input Reader
• agents, e.g., Paginator, which computes document
  page breaks, or InputReader
• events and transactions, e.g., MouseEvent,Customer
  Arrival
• users and roles, e.g., Administrator, User
• systems, e.g., mailsystem (overall),
  InitializationSystem (initializes)
• containers, e.g., Mailbox, Invoice, Event
• foundation classes, e.g., String, Date, Vector,
  etc.

9
Sequence Diagram
Sequence Diagram a sequence diagram also
models dynamic behavior typically a sequence
diagram shows how objects act together to
implement a single use case messages passed
between the objects are also shown sequence
diagrams help to show the overall flow of control
in the part of the program being modeled they
can also be used to show concurrent
processes asynchronous behavior
10
Sequence Diagram--Syntax
Objects in the sequence diagram are shown as
boxes at the top below each object is a dashed
vertical line--the objects lifeline an arrow
between two lifelines represents each
message arrows are labeled with message names
and can also include information on arguments and
control information two types of
control condition, e.g., is greaterthan
zero iteration, e.g., for all array
items return arrows can also be included
11
Sequence Diagram Exampletext, chapter 5
12
showing a branch in a UML sequence
diagramhttp//stackoverflow.com/questions/81147
70/how-to-show-if-condition-on-a-sequence-diagram
13
Looping in a sequence diagramhttp//www.ibm.com/
developerworks/rational/library/content/RationalEd
ge/feb04/3101_figure10.html
14
Example sequence diagram for example use case
developed in last class
15
ER diagrams

• Useful object relationships
• These diagrams represent the relationships
  between the classes in the system. These
  represent a static view of the system.
• There are three basic types of relationship
• inheritance ("is-a") (NOT the same as use case
  inheritance)
• aggregation ("has-a)
• association ("uses")
• These are commonly diagrammed as follows

16
ER diagram is-a
is-a draw an arrow from the derived to the base
class
17
ER diagram--has-a
has-a draw a line with a diamond on the end at
the "container" class. Cardinalities may also be
shown (11, 1n, 10m 1, i.e., any number gt
0, 11, i.e., any number gt 1)
tire car can exist independentlyshared
aggregation
person
arm is part of the person composition aggregation
arm
1 2
18
ER diagram--uses
uses or association there are many ways to
represent this relationship, e.g.,
employs
1
company
car
gasstation



n
employee
1
works for
19
CRC cards
CRC cards class--responsibilities--collaborators
cards "responsibilities" operators,
methods "collaborators" related classes (for
a particular operator or method)
Make one actual card for each discovered class,
with responsibilities and collaborators on the
front, data fields on the back. CRC cards are
not really part of UML, but are often used in
conjunction with it. The CRC card contains
information about what is inside the class (data,
structures, methods).
20
CRC card--example
Example (based on Horstmann, Practical
Object-Oriented Development in C and Java)
front back
Class Mailbox
Queue of new messages Queue of kept
messages Greeting Extension number Passcode
Note Bruegge Dutoit DO NOT include CRC
cards(they do show some internal information on
their class boxes)YOU NEED TO USE CRC CARDS,
they provide more information
21
State Diagram
State Diagram another way of adding detail to
the design--models dynamic behavior describes
all the possible states a particular object can
be in and how that object's state changes as a
result of events that affect that object usually
drawn for a single class to show behavior of a
single object used to clarify dynamic behavior
within the system, as needed
22
State Diagram--Properties
A state diagram contains a "start" point, states,
and transitions from one state to another. Each
state is labeled by its name and by the
activities which occur when in that state.
Transitions can have three optional labels
Event Guard / Action. A transition is
triggered by an Event. If there is no Event,
then the transition is triggered as soon as the
state activities are completed. A Guard can be
true or false. If the Guard is false, the
transition is not taken. An Action is completed
during the transition.
23
State Diagram--Example
Example this state diagram example for an
"order" in an order-processing system is from
Fowler and Scott, UML Distilled (Addison-Wesley,
1997)
start
/get first item
not all items checked /get next item
all items checked all items available
Dispatching
Checking
initiate delivery
check item
all items checked some items not in stock
delivered
item received all items in stock
Delivered
Waiting
item received some items not in stock
24
Examplebank simulation (Horstmann)
Horstmann, Mastering Object-Oriented Design in
C, Wiley, 1995
Teller 1
Teller 2
Customer 1
Customer 3
Customer 2
Teller 3
Teller 4
25
Examplebank simulation (Horstmann), cont.
An initial solution (Horstmann, p. 388)
26
Examplebank simulation (Horstmann), cont.
An improved solution (Horstmann, p. 391)
27
Comparison
What simplifications have been made? Why?
28
Example (revisited) How would we use the tools
described so far to design a state-of-the art
vending machine? How would we develop test cases
at each stage? Use cases? Class
diagram? Sequence diagram? Classes / CRC cards?