The avid reader will probably be wondering what all of this has to do with Aggregates and Aggregate Design. And actually, that's a pretty good question. There's a direct relation, so let's explore it. The Relational Model uses tables to store data. Those tables are composed of rows, where each row usually represents an instance of a concept of the application's interest. Additionally, each row can point to other rows on other tables of the same database, and the consistency between this relationship can be kept by the use of referential integrity. This model is fine; however, it lacks a very basic word: the object word.

Indeed, when we talk about the Relational Model, we're namely talking about tables, rows, and relationships between rows. And when we talk about the Object-Oriented Model, we're talking mainly about compositions of objects. So every time we fetch data — a set of rows — from a relational database, we run a translation process responsible for building an in-memory...