As you’ve seen in the previous chapter, organizing the structure of a service is a complex matter: the number of parts, what duties they should have, the boundaries between them—it all has to be carefully considered. The focus of DDD was mainly on language and boundaries and cooperation between domain experts and tech experts, but it also offered some sort of direction on how to organize the code. In fact, we talked about layers, but we never explained what they are and let you have an instinctive idea of what they mean.