Learning Domain-Driven Design

When exploring possible decomposition options, resolve to the principles behind what the bounded context pattern is based on: Why is it better to design problem-oriented models instead of a single model for all use cases? Because “all-in-one” solutions are rarely effective for anything. Why can’t a bounded context host conflicting models? Because o

Ironically, the projects that can benefit from DDD the most are the brownfield projects: those that already proved their business viability and need a shake-up to fight accumulated technical debt and design entropy. Coincidentally, working on such brownfield, legacy, big-balls-of-mud codebases is where we spend most of our software engineering care

As the name suggests, supporting subdomains support the company’s business. However, contrary to core subdomains, supporting subdomains do not provide any competitive advantage.

All stakeholders should consistently use the ubiquitous language in all project-related communications to spread knowledge about and foster a shared understanding of the business domain. The language should be continuously reinforced throughout the project: requirements, tests, documentation, and even the source code itself should use this language

At times it may be challenging to differentiate between core and supporting subdomains. Complexity is a useful guiding principle. Ask whether the subdomain in question can be turned into a side business. Would someone pay for it on its own? If so, this is a core subdomain. Similar reasoning applies for differentiating supporting and generic subdoma

We can use the definition of “subdomains as a set of coherent use cases” as a guiding principle for when to stop looking for finer-grained subdomains.

When discussing tactical design patterns, don’t appeal to authority: “Let’s use an aggregate here because the DDD book says so!” Instead, appeal to logic. For example: Why are explicit transactional boundaries important? To protect the consistency of the data. Why can’t a database transaction modify more than one instance of an aggregate? To ensure

Generic subdomains are business activities that all companies are performing in the same way. Like core subdomains, generic subdomains are generally complex and hard to implement. However, generic subdomains do not provide any competitive edge for the company. There is no need for innovation or optimization here: battle-tested implementations are w

As Alberto Brandolini1 says, software development is a learning process; working code is a side effect. A software project’s success depends on the effectiveness of knowledge sharing between domain experts and software engineers. We have to understand the problem in order to solve it.