1. Object-Oriented Design
IT4GIS
Keith T. Weber, GISP
GIS Director
ISU-GIS Training and Research Center

2. Topics
During the balance of this semester, we will pursue and follow two learning threads
Object-relational databases
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
The first PC’s did not have an OS. They had a BIOS and that is where the user (programmer) interfaced. Programs were small, difficult, and quirky. Because PC’s were not really capable of much (kind of a hobbyists toy…like a ham radio operator) programs were simple things. Like printing text on the screen for someone to read. Adding numbers together (a very expensive calculator which required hours of programming to even enable the calculator to work).
Programs were written sequentially with line numbers.
More complicated programs…those that could NOT be purely sequential because they involved decisions (do you want to add OR subtract) needed to use GOTO statements. Soon the simple sequential programs were bogged down with tons of GOTO’s and the flow was a messy (making them unstable). This programming style was later dubbed spaghetti programming.

5. The concept of encapsulation!
Why…Object-Oriented
A brief history of computer programming…
The concept of encapsulation!
As programs grew larger and more complex AND interacted with the OS and other apps more, the need was born to develop programs in re-usable modules or packets. Thereby reducing redundancy and the program footprint, while increasing the computer users learning curve through the development of common/similar tools (open, save, print, etc)

6. Today’s Goals
We will dissect “Object-Oriented” to learn what it really is and how it relates to object-relational databases
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 in a cohesive package
Some are concrete (i.e., real world)
Bank account
Rental item
Database item
Pile
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 approach can allow one to create a list of candidate classes

9. What is an OBJECT An instance of a CLASS That contains meaningful data
OBJECTS occupy memory space at runtime
If not, they are CLASSES
For example: data type vs. double
Data type is a class. It exists as a concept and can be used by programmers and GIS analysts, but does not require computer resources until actually used such as when one declares a field as a double in a database table.

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

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

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

13. Questions so far…
Give tour

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. Inheritance in the Geodatabase

16. Defining a CLASS After a class has been identified we can define:
The behavior of each class
Methods (verbs)
And the attributes of each class

17. Behavior

18. Relationships Between CLASSES
We have learned about inheritance as one (1) relationship between classes
There are three (3) important relationships
Inheritance
Aggregation
Dependency

19. 1- Inheritance Is-a relationship
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. 2- Aggregation Has-a relationship
Each Dog has a Paw (dog is not a generalization of paw!)
One class (Appendages) contains references to another class (Dog)

21. Inheritance vs. Aggregation
Often confused
Questions?

22. Example Car is a Vehicle – Inheritance
Car has a set of Tires – Aggregation

23. 3- Dependency
Dependency occurs when a class uses or relies on another class
This is a Uses relationship
Example: an application may depend on the Scanner class to read input

24. What type of Method behaviors are these?
Class Diagram
What type of Method behaviors are these?
Dependency…a deposit uses a bank account (cannot happen without it)

25. Attributes

26. Class Diagram
Attributes help define a given class and instantiate it into an object
Dependency…a deposit uses a bank account (cannot happen without it)

27. Dog example Name of the class = Methods= Dog Attributes?
Example of inheritance
Example of aggregation
Example of dependence
Attributes?
Dog
Brainstorm some methods.
Inherited methods (is a) inherit from? Animal. What can it inherit from animal. Circulatory system, nervous system…etc. Maybe we need another superclass between animal and dog called mammal?
Aggregated methods (has a) paw
Dependency (uses) Bark needs a dog...dog class uses the bark class (superclass subclass structure)
Health: height, weight, health, name (note, these attributes are not set as they would require memory and computer resources, so they have no state as a class)

28. Instantiate into an object
Three features characterize objects:
Identity: specific attribute (property) settings have been made for the class. This distinguishes it from all other objects.
State: Describes the data stored in the object WHERE DID THIS COME FROM?
Behavior: describes the method in the object's interface through which the object can be used (how do we make the dog bark?)
Only an instantiated class (an object) can have a state. It is active and dynamic. If something has a state (status) then it is an object, not a class.

29. Instantiating the Dog CLASS
CLASS (DOG)
Attributes (Properties)
NAME = Scooby-Doo
HEIGHT = 36
WEIGHT = 145
Methods
[Uses] bark- “Rooby roo”
etc.
Scooby-Doo
Notice, the properties have a state. This is an object…an instantiation of the dog class.

30. 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
Inheritance, aggregation, dependency

31. Questions…
Give tour