1. Representing Structure and Behavior
CS1316: Representing Structure and Behavior

2. Story Techniques for representing data structure
Arrays, linked lists, circular linked lists, trees, graphs, stacks, queues, event queues
Techniques for representing behavior
Functions (in Python), methods (in Java)
Techniques for representing both
Objects (what they know, and what they know how to do)
Simulations
Functional branches in a tree
Messages in a simulation
Techniques for describing structure and behavior outside a program
UML class diagrams, Abstract Data Types (ADTs)
What’s a program?

3. The Point of this Course
Real computer-based media developers rarely work in terms of pixels and samples
Computer musicians deal in terms of notes, instruments, patches, and other structures.
Computer animators deal in terms of characters, movement, scenes, and other structures
Bottom-line: They structure their media.

4. Driving Questions of the Course
How did the wildebeest’s charge over the ridge in The Lion King?
How did the villages wave in The Hunchback of Notre Dame?

5. The Wildebeests in The Lion King

6. The Villagers in The Hunchback of Notre Dame

7. The answer: Modeling and Simulation
These are two of the (rare) times that Disney stepped away from their traditional drawn cel animation.
Instead they:
Modeled the structure of wildebeests and villagers,
Modeled the behavior of wildebeests (how they stampede) and villagers (how they wave),
Then started a computer simulation that executed the models…and basically filmed the screen.

8. How did they do that?

9. Data structures and their properties: Arrays
Arrays are efficient in memory
Everything is packed together
Uses no additional memory
Very fast for accessing any individual element
They are hard to insert and delete with.
Have to move everything around
They can’t be grown.
They have a fixed size.

10. Linked Lists Uses extra memory to record next
Simple to insert and delete elements within
Reconnect, disconnect
Have to find elements to access them
Can grow as large as memory allows

11. Circular linked lists Good for describing data that loops
But don’t try to traverse them using any normal traversal!

12. Trees Uses branch nodes that represent both next but children.
In binary trees, every node represents left and right.
All the advantages of linked lists, but can also representing hierarchy or clustering.

13. Graphs Like trees, but arbitrary linking.
Anything can link to anything else, including loops.
Good for representing things like highway systems and blood paths and other real things.

14. Stack A LIFO (Last In First Out) list.
We described it as an ADT (Abstract Data Type)
What methods it understands (push, pop, peek, size, empty)
What those methods do.
We used it for reversing a list.

15. Queue A FIFO (First In First Out) list We described it as an ADT, too.
We used it to represent agents lining up for a resource in a simulation

16. Event Queue It’s a queue where elements are kept in a sorted order.
For us, it was in order of event times.
We needed the earliest time to be at the top of the queue.

17. Representing behavior
Functions in Python describe behavior.
They take data in as input and act upon it
Sometimes returning other data
Methods in Java describe behavior
They can act just like functions, but they can also manipulate this—the object that the method is part of.

18. ADT’s Describing the methods Describing how they work
Push, pop, peek, size, empty
Describing how they work
Pop off the head
Push onto the tail
If you write your programs expecting any implementation of a given ADT, your program will work even when the ADT implementation changes.

19. Representing both Objects
Keep instance (and class “static”) data and its structure—what they “know”
Keep methods for describing behavior on that data—what they “know how”
Objects represent both structure and behavior
Objects were originally invented in order to do simulations.
All programs can be thought of as simulations.

20. Embedding behavior in our structures
Branches in trees that manipulate their children
Scaling in sound trees
Moving and vertical/horizontal placement in picture trees
Messages in simulations are data that trigger behavior
“Now, you’re at the factory”

21. How do we describe this stuff?
Describing structure and behavior is modeling
Obviously, a program can, but that’s a very detailed description.
Anything easier to grasp, to see without so much implementation detail? I

22. UML class diagrams
Represent both structure and behavior

23. What’s a program? As we started with in CS1315:
A program is a specification of process, so exact that it can be executed by a machine.
It’s the same thing now, at the end of CS1316.
But…

24. Where’s the program?
The program is embedded in representations of structure and behavior.
It’s in that tree that holds your hierarchy.
And in those messages that tell your agents what to do.
And in how that queue works.
And throughout the insertAfter(), and add(), and last() and other methods of your data structures.
And in ALL those objects that you create and use.
Programs are distributed across your representations of structure and behavior.
In a real sense, “Representing Structure and Behavior” means “Advanced Programming.”