ch 5 o o data modeling
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Object-Oriented Data Object-Oriented Data ModelingModeling
Modern Database Management
Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden
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What is Object Oriented Data Modeling?What is Object Oriented Data Modeling? Centers around objects and classes Involves inheritance Encapsulates both data and behavior Benefits of Object-Oriented Modeling
– Ability to tackle challenging problems– Improved communication between users, analysts, designer, and
programmers– Increased consistency in analysis and design– Explicit representation of commonality among system components– System robustness– Reusability of analysis, design, and programming results
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Figure 14-1 –Phases of object-oriented systems development cycle
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OO vs. EER Data ModelingOO vs. EER Data Modeling
Object Oriented EER
Class Entity typeObject Entity instanceAssociation RelationshipInheritance of attributes Inheritance of attributesInheritance of behavior No representation of
behavior
Object-oriented modeling is frequently accomplished using the Unified Modeling Language (UML)Unified Modeling Language (UML)
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ObjectObjectAn entity that has a well-defined role in the
application domain, as well as state, behavior, and identity– Tangible: person, place or thing– Concept or Event: department, performance,
marriage, registration– Artifact of the Design Process: user interface,
controller, scheduler
ObjectsObjects exhibit BEHAVIOR as well as attributes Different from entitiesentities
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State, Behavior, IdentityState, Behavior, Identity
State: attribute types and valuesBehavior: how an object acts and reacts
– Behavior is expressed through operations that can be performed on it
Identity: every object has a unique identity, even if all of its attribute values are the same
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Figure 14-2 –UML class and object diagrams
(a) Class diagram showing two classes
Class diagramClass diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.
Behavior
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(b) Object diagram with two instances
Object diagramObject diagram shows instances that are compatible with a given class diagram.
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OperationsOperations A function or service that is provided by all
instances of a class Types of operators:
– ConstructorConstructor: creates a new instance of a class– QueryQuery: accesses the state of an object but does not alter
its state– UpdateUpdate: alters the state of an object– ScopeScope: operation applying to the class instead of an
instance
Operations implement the object’s behaviorbehavior
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AssociationsAssociations
AssociationAssociation: – Relationship among object classes
Association RoleAssociation Role:– Role of an object in an association – The end of an association where it connects to a
classMultiplicityMultiplicity:
– How many objects participate in an association. Lower-bound..Upper bound (cardinality).
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Figure 14-3 –Association relationships of different degrees
Lower-bound – upper-bound
Represented as: 0..1, 0..*, 1..1, 1..*
Similar to minimum/maximum cardinality rules in EER
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Figure 14-4 – Examples of binary association relationships (a) University example
Alternative multiplicity representation: specifying the two possible values in a list
instead of a range
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(b) Customer order example
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Figure 14-5 –Object diagram
for customer order example
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Association ClassAssociation Class
An association that has attributes or operations of its own or that participates in relationships with other classes
Like an associative entity in ER model
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Figure 14-6 – Association class and link object
(a) Class diagram showing association classes
Binary association class with behavior
Unary association with only attributes and no behavior
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Figure 14-7 –Ternary relationship with association class
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Figure 14-8 – Derived attribute, association, and role
Derived attributes an relationships shown with / / in front of the name
Derived relationship (from Registers-for and Scheduled-for)
Constraint expression for derived attribute
Derived attribute
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Generalization/SpecializationGeneralization/Specialization
Subclass, superclass– similar to subtype/supertype in EER
Common attributes, relationships, AND operations
Disjoint vs. Overlapping Complete (total specialization) vs. incomplete
(partial specialization) Abstract Class: no direct instances Concrete Class: direct instances
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Figure 14-9 – Examples of generalization, inheritance, and constraints
(a) Employee superclass with three subclasses
Shared attributes and operations
An employee can only be one of these subclasses An employee
may be none of them.
Specialized attributes and operations
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(a) Abstract patient class with two concrete subclasses
Abstract indicated by italics
Dynamic means a patient can change from one subclass to another over time
A patient MUST be EXACTLY one of the subtypes
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Class-Level AttributeClass-Level Attribute
Specifies a value common to an entire class, rather than a specific value for an instance.
Represented by underlining
“=“ is initial, default value.
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PolymorphismPolymorphism
Abstract Operation: Defines the form or protocol of the operation, but not its implementation.
Method: The implementation of an operation.
Polymorphism: The same operationmay apply to two or more classes in
different ways
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Figure 14-11 – Polymorphism, abstract operation, class-scope attribute, and ordering
Class-level attributes – only one value common to all instances of these clases
This operation is abstract…it has no method at Student level
Methods are defined at subclass level
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Overriding InheritanceOverriding Inheritance
Overriding: The process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass.– For Extension: add code.– For Restriction: limit the method. – For Optimization: improve code by exploiting
restrictions imposed by the subclass.
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Multiple InheritanceMultiple Inheritance
Multiple Classification: An object is an instance of more than one class.
Multiple Inheritance: A class inherits features from more than one superclass.
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Figure 14-13 Multiple inheritance
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AggregationAggregation
Aggregation: A part-of relationship between a component object and an aggregate object.
Composition: A stronger form of aggregation in which a part object belongs to only one whole object and exists only as part of the whole object.
Recursive Aggregation: composition where component object is an instance of the same class as the aggregate object.
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Figure 14-14 – Example aggregation
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Figure 14-15 – Aggregation and Composition
(a) Class diagram
(b) Object diagram
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Figure 14-16 – Recursive aggregation
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Business RulesBusiness Rules See chapters 3 and 4 Implicit and explicit constraints on objects – for
example:– cardinality constraints on association roles– ordering constraints on association roles
Business rules involving two graphical symbols:– labeled dashed arrow from one to the other
Business rules involving three or more graphical symbols:– note with dashed lines to each symbol
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Figure 14-17 – Representing business rules
Three-symbol constraint
Two-symbol constraint
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Figure 14-18 –Class diagram for Pine Valley Furniture Company