Let's create a sample domain service based on our table-reservation system. As discussed in this chapter, the importance of an efficient domain layer is the key to successful products or services. Projects developed based on the domain layer are more maintainable, highly cohesive, and decoupled. They provide high scalability in terms of business requirement changes, and have a low impact on the design of other layers.
Domain-driven development is based on the relevant domain, hence it is not recommended that you use a top-down approach where the UI would be developed first, followed by the rest of the layers, and finally the persistence layer. Nor should you use a bottom-up approach, where the persistence layer, such as the DB, is designed first, followed by the rest of the layers, with the UI last.
Having a domain model developed first, using the patterns...
