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Object-Oriented Design

Object-Oriented Design. Keith T. Weber, GISP GIS Director, ISU. Topics. During the balance of this semester, we will pursue and follow two learning threads Object-relational databases And the Geo-Web These two threads are interwoven. To understand Object-Relational Databases….

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Object-Oriented Design

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  1. Object-Oriented Design Keith T. Weber, GISP GIS Director, ISU

  2. Topics • During the balance of this semester, we will pursue and follow two learning threads • Object-relational databases • And the Geo-Web • These two threads are interwoven

  3. To understand Object-Relational Databases… • We need to understand both relational concepts and • Object-oriented concepts (this week)

  4. The Early Days… • Computer programming from the caveman era

  5. Why…Object-Oriented • A brief history of computer programming… The concept of encapsulation!

  6. Today’s Goals • We will dissect “Object-Oriented” to learn what it really is and how it relates to object-relational databases, specifically… • What is a class? • What is an object? • Enable you to identify inheritance, aggregation, and dependency relationships between classes • Understand class attributes and object properties • Become familiar with new terminology

  7. What is a CLASS? • A class is a computer construct representing a concept bound (encapsulated) in a cohesive package • Some are concrete (i.e., real world) • Bank account • Rental item • Database item • Others are abstract • Scanner • Stream • Math

  8. Discovering CLASSES • Simple Rule: • Look for nouns in descriptions • Obviously not all nouns are classes • But at least this method can allow one to create a list of candidate classes

  9. What is an OBJECT • An instance of a CLASS • Contains meaningful data • OBJECTS occupy memory at runtime • If not, they are CLASSES • For example: data type vs. double

  10. Dog Scooby-Doo A little Quiz… • #1 Class or Object? Dog is a generalization of Scooby-Doo

  11. Dog Animal Scooby-Doo A little Quiz (cont’d)… • #2 Class or Object? Dog is a subclass of the Animal class Animal is a generalization of Dog The concept of subclass!

  12. Dog Animal Bird A little Quiz (cont’d)… • #3 Class or Object? The concept of polymorphism!

  13. Questions…

  14. Key Points • Many classes already exist and are at our disposal when we design a database • We use inheritance to add capabilities to our projects • A subclass inherits from its superclass • i.e., a child inherits from its parent

  15. Defining our CLASS • After a class has been identified we can define: • The behavior of each class • Verbs = methods • The attributes of each class

  16. Behavior

  17. Relationships Between CLASSES • We just mentioned inheritance as a relationship between classes • How classes relate to one another is called a behavior

  18. Three Relationship Behaviors • Inheritance • Aggregation • Dependency

  19. Inheritance • Is-arelationship • Relationship between a more general class (superclass) and a more specialized class (subclass) • Every… • savings account is a bank account • DVD rental is a rental

  20. Aggregation • Has-arelationship • Each Dog has a Paw (dog is not a generalization of paw!) • Objects of one class contain references to (or need) objects of another class

  21. Inheritance vs. Aggregation • Often confused • Questions?

  22. Example • Car is a Vehicle – Inheritance • Car has aTire – Aggregation

  23. Dependency • Dependency occurs when a class uses another class • This is a Uses relationship • Example: an application may depend on the Scanner class to read input

  24. Example: BankAccountClass Diagram What BEHAVIOR does deposit and withdraw represent?

  25. Attributes

  26. Example: BankAccountClass Diagram

  27. Dog Example: Dog • Name of the class = • Methods? • Attributes?

  28. Instantiation into an OBJECT • Three features characterize objects: • Identity: specific property settings have been made for the attributes of the class. This distinguishes it uniquely from other objects. • State: Describes the data stored in the object WHERE DID THIS COME FROM? • Behavior: describes the methods in the object's interface through which the object can be used.

  29. Scooby-Doo Instantiating the Dog CLASS • CLASS (DOG) • Attributes (Properties) • NAME = Scooby-Doo • HEIGHT = 36 • WEIGHT = 145 • Methods • [Uses] bark- “Rooby roo” • etc.

  30. Applying Object Oriented Skills: Reading a Business Statement

  31. Identify Candidate Classes • A candidate class may or may not remain a class throughout the design process • A candidate class may or may not become a table • Do not focus on tables at this point

  32. Locate Nouns • Classes are nouns • A noun is a “person, place, or thing”

  33. And now…Verbs • Candidate methods are verbs • They show action • They exhibit behaviors

  34. Methods • Identifying candidate methods allows us to better understand how the business operates and how the Enterprise uses GIS. • A method is a behavior…a relationship between classes • The candidate methods describe an inheritance, aggregation, or dependency relationship

  35. Key Concepts • Understand the difference between a CLASS and an OBJECT • Understand new terms: • Encapsulation, polymorphism, superclass, subclass, behavior, attributes, instantiation • Understand --and be able to differentiate-- the three types of behaviors

  36. Questions…

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