There is a reason why the nested structures recipe is right after that of joins. Nested structures have traditionally been associated with web-based applications and hyper-scale companies. The most common format of nested structures is JSON. JSON inherited nested structures from XML, which JSON made irrelevant.
The power of nested structures goes far beyond traditional use cases, though. It has been very difficult to represent hierarchical data in highly normalized databases. Data needs to be joined across tables as needed. This does provide us with flexibility. Let's understand it with the example we covered in the previous recipe. In the Yelp dataset, a user reviews a business, which is represented by yelp_academic_dataset_review.json. In reality, a user reviews multiple businesses and a business is reviewed by multiple users. One would argue that it represents standard NxN relationships between entities, so what's the big deal here? The challenges...