Domain models, such as Domain-Driven-Design require an ubiquitous / common language for all stakeholders (from business departments to developers and their code). The model generated of this language shall be shifted into the source code:
- Entities
like Business Objects. - Value Objects
like Data-Transfer-Objects (DTOs). - Services
which contain workflows and processing units. - Modules
Collection of Entities. - Aggregates
List of Entities. - Factories
Creates Entities. - Repositories
Location where objects and data is stored.
Types of Domains
There are many types of domains, which can be integrated by published language (such as XML-Schema), open host services (e.g. RESTfull web services), an Anti-Corruption-Layer or Separate Ways (no interaction of domains) pattern. Other approaches use Facades or Wrappers. Erich Gamma describes many good patterns. The most common domains are:
- Core Domain
contains core functionality of a system. These are the reason for the existance of the system and must be implemented by experienced developers. - Generic Subdomain
contains functionality, which is important for the business workflow, but are not part of the core domain. Examples are invoices or shipping of letters. Those modules can also be bought in from external (services). - Supporting Subdomain
contains supporting or subordinate functionality, which can be developed by less experienced developers. This domain must be strictly separated from the core domain, e.g. through an Anti-Corruption-Layer.