Database Management System
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Transcript of Database Management System
Database Management System
Prepared by Dr. Ahmed El-Ragal
Reviewed & Presented By Mr. Mahmoud Rafeek Alfarra
College Of Science & Technology Khan younisInformation Technology & Computer Science Dep.
Part 9Object-Oriented Database Modeling
What is Object Oriented Database 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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Overview
Object-oriented techniques work well in situations where complicated systems are undergoing continuous maintenance, adaptation, and design.
There are two ways to model object-oriented systems:Coad and Yourdon methodology.The Unified Modeling Language.
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6 ideas
Six ideas characterize object-oriented modeling:
An object, which represents a real-world thing or event.A class, or group of related objects.Messages, sent between objects.Encapsulation, only an object makes changes through its
own behavior.Inheritance, a new class created from another class.Polymorphism, meaning that a derived class behavior
may be different from the base class.
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Naming
Another name for property is attribute.Another name for method is operation.
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OO vs. EER Data Modeling
Object Oriented
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EER
Object Class Entity typeObject Instance Entity instanceAssociation RelationshipInheritance of attributes Inheritance of attributesInheritance of behavior No representation of behavior
Object
An 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.
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ObjectsObjects exhibit BEHAVIOR as well as attributes Different from entitiesentities
State, Behavior, Identity
State: attribute types and values.
Behavior: how an object acts and reacts.Behavior is expressed through operations that can
be performed on it.
Identity: every object has a unique identity.
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Five-Layer Model
Object oriented analysis and design is based on a five-layer model:Class/object layer notes the classes and objects.Structure layer captures various structures of classes
and objects, such as one-to-many relationships and inheritance.
Attribute layer details the attributes of classes.Service layer notes messages and object behaviors.Subject layer divides the design into implementation
units or team assignments.
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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.
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(b) Object diagram with two instances
Object diagramObject diagram shows instances that are compatible with a given class diagram.
Operations
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.
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Operations implement the object’s behaviorbehavior
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Encapsulation
An object is an encapsulated structure, having both attributes and methods.
The term encapsulation means that it is complete in itself. Programs external to an object know nothing of its structure and
need to know nothing of that. The external appearance of an object is referred to as interface. The interface consists of attributes and methods that are visible to
the outside world. The encapsulated internal structure of an object is referred to as
implementation. An OO object may have a method to create itself, display itself,
and modify itself. Any of these methods is a program. OO objects interact by calling each other’s methods. Since all
objects are encapsulated none need to know others’ structure.
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Associations
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 class
MultiplicityMultiplicity: How many objects participate in an association.
Lower-bound..Upper bound (cardinality).
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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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Examples of binary association relationships (a) University example
Alternative multiplicity representation: specifying the two possible values in a list
instead of a range
Association ClassAn 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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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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(b) Object diagram showing link objects
Association class instances
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Derived attribute, association, and role
Derived attributes and relationships shown with / / in front of the name
Derived relationship (from Registers-for and Scheduled-for)
Constraint expression for derived attribute
Derived attribute
Generalization/SpecializationSubclass, superclass
similar to subtype/supertype in EERCommon attributes, relationships, AND
operationsDisjoint vs. OverlappingComplete (total specialization) vs.
incomplete (partial specialization)Abstract Class: no direct instances???Concrete Class: direct instances???
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Class-Level AttributeSpecifies 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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PolymorphismAbstract Operation: Defines the form or
protocol of the operation, but not its implementation.
Method: The implementation of an operation.
Polymorphism: The same operation may apply to two or more classes in different ways.
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Overriding 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 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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Multiple inheritance
AggregationAggregation: 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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Example aggregation
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Aggregation and Composition
(a) Class diagram
(b) Object diagram
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Recursive aggregation
Reviewed By Mr. Mahmoud Rafeek Alfarra