Core Data - iOS Programming: The Big Nerd Ranch Guide - page 482

The model file
In a relational database, we have something called a table . A table represents some type;
you can have a table of people, a table of a credit card purchases, or a table of real-estate
listings. Each table has a number of columns to hold pieces of information about that
thing. A table that represents people might have a column for the person's name, social se-
curity number, height, and age. Every row in the table represents a single person.
Figure 16.2 Role of Core Data
This organization translates well to Objective-C. Every table is like an Objective-C class.
Every column is one of the class's instance variables. Every row is an instance of that
class. Thus, Core Data's job is to move data to and from these two organizations ( Fig-
ure 16.2 ) .
Core Data uses different terminology to describe these ideas: a table/class is called a en-
tity , and the columns/instance variables are called attributes . A Core Data model file is the
description of every entity along with its attributes in your application. In Homepwner ,
you're going to describe a BNRItem entity in a model file and give it attributes like
itemName , serialNumber , and valueInDollars .
Open Homepwner.xcodeproj . From the File menu, create a new file. Select Core
Data in the iOS section and create a new Data Model . Name it Homepwner .
Figure 16.3 Create the model File