Understand the problem: To have a deep, shared understanding of the problem, it is necessary for business and technology experts to collaborate closely. Here, we collectively understand what the problem is and why it is valuable to solve. This is termed the domain of the problem.
Break down the problem into more manageable parts: To keep complexity at manageable levels, break down complex problems into smaller, independently solvable parts. These parts are termed subdomains. It may be necessary to further break down subdomains where the subdomain is still too complex. Assign explicit boundaries to limit the functionality of each subdomain. This boundary is termed the bounded context for that subdomain. It may also be convenient to think of the subdomain as a concept that makes more sense to the domain experts (in the problem space), whereas the bounded context is a concept that makes more sense to the technology experts (in the solution space).
For each of these bounded contexts, do the following:
Agree on a shared language: Formalize the understanding by establishing a shared language that is applicable unambiguously within the bounds of the subdomain. This shared language is termed the ubiquitous language of the domain.
Express understanding in shared models: In order to produce working software, express the ubiquitous language in the form of shared models. This model is termed the domain model. There may exist multiple variations of this model, each meant to clarify a specific aspect of the solution, for example, a process model, a sequence diagram, working code, and a deployment topology.
Embrace the incidental complexity of the problem: It is important to note that it is not possible to shy away from the essential complexity of a given problem. By breaking down the problem into subdomains and bounded contexts, we are attempting to distribute it (more or less) evenly across more manageable parts.
Continuously evolve for greater insight: It is important to understand that the previous steps are not a one-time activity. Businesses, technologies, processes, and our understanding of these evolve, so it is important for our shared understanding to remain in sync with these models through continuous refactoring.