Transcript Object Oriented Design

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Week08
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Review Schedule Weeks 8-14
This week
o Review last class
o Introduce Class Diagrams
o ICE-03
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Identify and analyze the objects and object-classes needed in a
system
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Learn how to identify and represent relationships between
object classes.
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Learn how to identify and create super/subclass relationships
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Learn how to create a Unified Modeling Language (UML) class
diagram using System Architect
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Use case
o Activity the system carries out
o Entry point into the modeling process
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Event decomposition: help identify use cases
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Elementary business processes (EBPs)
o Basic unit of analysis
o Initiated by event occurring at specific time and place
o Discrete system response that adds business value
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Event decomposition
o Develops use cases based on system response to events
o Focus on business processes and business requirements
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Result of the decomposition:
o List of use cases triggered by business events
o Use cases at the right level of analysis
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Problem domain
o Set of work-related “things” in system component
• Things have data representation within system
o Examples: products, orders, invoices, customers
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OO approach to things in problem domain
o Objects that interact in the system
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Identify and understand things in problem domain
o Key initial steps in defining requirements
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Things can be identified with methodology
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Separate the tangible from the intangible
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Include information from all types of users
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Ask important questions about nature of event
o “What actions upon things should be acknowledged and
recorded by the system?”
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List nouns users mention when discussing system
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Event table as source of potential things
o Use cases, external agents, triggers, response
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Select nouns with questions concerning relevance
o Further research may be needed
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Analyst document entity associations ( relationships)
o Example: “Is placed by” and “works in”
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Associations apply in two directions
o Customer places an order
o An order is placed by a customer
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Multiplicity: the number of associations
o One to one or one to many
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The associations between types of things
o Unary (recursive), binary, n-ary
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Associations Naturally Occur between Things
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Multiplicity of Relationships
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Specific details of things are called attributes
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Analyst should identify attributes of things
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Identifier (key): attribute uniquely identifying thing
o Examples: Social Security number, vehicle ID number, or
product ID number
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Compound attribute is a set of related attributes
o Example: multiple names for the same customer
Sheridan
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Sheridan
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Domain model class diagram as UML class
o OOA applies domain model class diagram to things
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Problem domain objects have attributes
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Software objects encapsulate attributes and
behaviors
o Behavior: action that the object processes itself
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Software objects communicate with messages
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Information system is a set of interacting objects
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Generalization/specialization notation
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Inheritance hierarchy
o Rank things the more general to the more special
• Motor vehicle class includes trucks, cars, buses
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Classification: means of defining classes of things
o Superclass: generalization of a class
o Subclass: specialization of a class
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Sheridan
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See SLATE
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Construct a class diagram from a narrative including
relationships and multiplicities.
 Identify and represent inheritance hierarchies in a
class diagram.
 Learn what is meant by a concrete and/or abstract
class.
 How to determine and note the constraints for
generalization / specialization relationships.
 Learn how to describe Whole-to-Part relationships on a
class diagram.
 How to draw all these relationships using System
Architect.
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Document the static
structure of the system
They define what classes
there are and how they are
related
The symbol on the right
defines the data and
behaviour encapsulated by a
class.
Objects “know things and
know how to do things!”
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Demo exercise
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From last class…
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We need to know what types of things the user works with
routinely.
o Many types
• Tangible
• Intangible
• Important to include information from all types of users
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Jacobson’s Three Types
Of Objects
•Entity
•Interface
•Control
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Attributes
Behavior (methods & operations)
o Real world
o Data world
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Class Diagram
Showing Two
Classes
Object Diagram
with Two Instances
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relationship among
object classes
 solid line connecting
classes
 association is named
i.e. drives
 where line connects to
class is called
“association role”
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shows number of objects in
an association
lower..upper bound
bounds are inclusive 2..5
0..1 = optional one
0..* = optional many
1..* = many
1 = exactly one
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Examples
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SLATE – Lesson 08 Class Diagram Exercises
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Some instances of a class (subclass) may be grouped
together based on features not shared by the rest of the
class.
o Attributes
o Behavior
o Relationships
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Key verb is “isakinda” (and inverse, “canbea”).
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A subclass is made up of
selected instances from
another class, the “Parent
class” or “superclass.”
A superclass includes all the
instances of the subclass,
plus possibly more as well.
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Each subclass then adds
attributes and behaviors
that it needs but the other
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Inheritance is when a
subclass instance, in
addition to the attributes
and behavior it has by
virtue of being in the
subclass, also has all the
attributes and behavior that
instances of the superclass
have.
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The subclass
relationship actually is
a relationship in the
way we have used that
word.
 It requires a verb (one
in each direction).
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o “isakinda”
o “canbea”
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To be considered truly O-O, a language, database, etc. must
support:
o Objects,
o Classes,
o Inheritance, and
o Polymorphism
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With subclasses, we can show more
detail about relationships on our
diagram.
For instance, in most companies,
only managers can hire and fire.
o In other words, only certain kindsa
employees can do certain tasks.
(only a baker can bake)
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We are able to show that some
relationships affect only a subclass,
not every instance.
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SLATE- Inheritance Exercise
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generalization path
o solid line with hollow
arrowhead pointing from
subclass to superclass
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indicate basis of
generalization
name the path for the
attribute being removed =
called the discriminator
discriminator shows which
property is abstracted by a
generalization relationship
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constraints on the subclasses
overlapping: descendent may
be descended from more than
one of the subclasses
o student can be both a
research and teaching
assistant
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disjoint: descendent may not
be descended from more than
one of the subclasses
o patient can not be both out
and resident
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complete: all subclasses
are listed
o only have out and resident
patients
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incomplete: all subclasses
are not listed
o more subclasses are
available
o can have casual, part-time
employees
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SLATE – Lesson 5 Vehicle Registration System
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Continue with relationships
o Class diagram
• Whole-Part associations (Aggregation)
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SYST30009 - Engineering Quality
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