1. CS3220 Web and Internet Programming About Data Models
Chengyu Sun
California State University, Los Angeles

2. Broadly speaking, the world
consists of things and actions
performed by things or on things

3. Things and Actions in Computer Programs
Most of computer programs are created to help people solve problems in the real world (or in the case of video games, problems in imaginary worlds)
Real World
Computer Program
Things
Data
Actions
Actions (Operations)

4. Data and Operations in Programming Languages
Values (a.k.a. Literals)
Variables
Structs
Data
Functions
Methods
Operations

5. Data and Operations in OO Languages
Class {
Fields
Methods }
Data
Operations

6. Data and Operations in MVC
A class that represents
only data
Model
Displays the result of
an operation
View
Controller
Implements an operation

7. Importance of Data Modeling
Data is half of your application
If data is not modeled correctly, operations will be wrong no matter what you do

8. What's Wrong with the Code?
List<String> surveys = new ArrayList<String>();
List<String> questions = new ArrayList<String>();
List<String> choices = new ArrayList<String>();

9. What's Wrong with the Code?
public class Survey {
String name;
List<String> questions;
List<String> choices; }

10. What's Wrong with the Code?
public class Survey {
String name;
String question;
List<String> choices; }

11. What's Wrong with the Code?
public class Survey {
String name;
Map<String, List<String>> questions; }

12. Create Data Model Classes
Look for nouns in the problem description
Simple types (e.g. number, string, data/time) become fields
Complex types (i.e. things that contain other things) become classes
Add an id field when necessary
If it passes the "English test", it's probably a good class