• DDD is a software development approach that uses and builds upon OO design principles.
• The standard definition of the domain is the “sphere of knowledge and activity around which the application logic revolves.”
  • It refers to the subject area to which the application is intended.
• DDD is a way of designing software that centers decision-making on the business domain, not the database schema or the latest framework.
• It insists that engineers collaborate deeply with domain experts during the project lifecycle, not just to gather requirements once and vanish into Jira tickets.
• It gives teams the vocabulary, patterns, and boundaries to model complex systems without getting buried in accidental complexity.
• The DDD approach becomes especially valuable when:
  • The domain is non-trivial and keeps evolving. Think finance, healthcare, logistics, or giant marketplaces.
  • Multiple teams are working on overlapping parts of the system.
  • Code needs to reflect real-world behavior, not abstract technical constructs.
• DDD doesn’t care whether the architecture is monolithic or microservice-based.
  • It does care about whether the model reflects the domain's real-world rules and language and whether it can evolve safely as the domain changes.
• DDD focuses on three essential outcomes:
  • Deep alignment between developers and domain experts.
    • The system only behaves correctly when everyone agrees on what “correct” means.
    • That shared understanding has to show up in both conversation and code.
  • Clean separation of concerns.
    • The business rules defining the system's behavior must be isolated from glue code, infrastructure, or delivery details.
    • They deserve to live in their own space.
  • Explicit boundaries around different parts of the domain.
    • Not everything fits into one giant model.
    • Different system areas often follow different rules, workflows, and terms.
    • DDD makes those differences explicit and enforces them with transparent edges.

Core Principles

• Focus on the core domain and domain logic.
• Base complex designs on models of the domain.
• Constantly collaborate with domain experts to improve the application model and resolve any emerging domain-related issues.

Common Terms

• Domain: The problem space that should be solved by designing a software.
• Context: The setting in which a word or statement appears determines its meaning.
  • Statements about a model can only be understood in a context.
• Model: A system of abstractions that describes selected aspects of a domain and can be used to solve problems related to that domain.
• Ubiquitous Language: A language structured around the domain model used by all team members to connect all the team activities with the software.
  • This language should resemble the business domain's terms, entities, and processes.

Bounded Context