Database Schema questions for creating an online shopping site

[johnmerlino]

Hey all,

 

I'm trying to get a good grasp of database structures out there for online shopping sites. I found this one:

http://www.databaseanswers.org/data_models/newegg/index.htm

 

However, it doesn't make sense to me:

1) It gives for_sale a foreign key of top_level_item_id to associate it with the top_level_items table. So it is creating a has many relationship where an item can have many sales. I understand how an item can have many sales?

2) How is it making the connection between top_level_items and entry_types through entry_type_code? Isn't is supposed to be entry_type_id?

 

Thanks for any response.