So when we talk about books, each book is made up of different parts, kind of like how you are made up of different body parts like arms, legs, and a head. These parts that make up a book are called components. For example, the pages inside the book, the cover, and the spine are all components of a book.
Now, sometimes we need to talk about a specific part of a book, like a specific page or a specific section of the cover. We use something called an item identifier for that. It's like a special name or number that helps us know exactly which part of the book we are talking about.
And finally, sometimes we need to talk about a specific copy of a book, like a copy that is in a library or a copy that you have at home. We use something called a book identifier or a book ID for that. It's like a special code that helps us know which exact copy of the book we are talking about.