DDD: Summary
Here is a summary / cliff’s notes of the Domain Driven Design Quickly eBook
Domain is what you trying to encode for which is owned by domain experts/specialist of the area
The domain model is an abstraction represents the domain you’re trying to capture from the owners
The domain model should be described and communicated within a ubiquitous language
An analyst model is independently derived from the domain not considering software and design
Layers of DDD: UI; Application; Domain; Infrastructure;
Entities are components that have identities and are mutable
Value Objects are immutable attributes or components that enrich entities and immutable
Aggregates is a single unit of change that own several entities of a domain model
An Aggregate root is an entity conduit for external requests policing change to a model
Services provide functionally at the application level or domain level with Aggregates
Factories are used to create complicated aggregates and tightly coupled to to the domain
Repositories are an abstraction of storage, retrieval and reconstitution of entities, coupled with infrastructure
Iterative and continuous Refactoring provide deeper insights, refine inconsistencies or missing components while avoiding a rigid design and improving to an incisive, deep model
Make constraints (invariables), process (methods or services) and (composable) specifications explicit
A Bounded Context is a logical frame allowing model evolution, isolation by module, team, code and DB schemas. CI fosters independent, pure and unified growth but doesn’t handle Inter-model relationships which should be well defined
A Context Map show relationships between bounded contexts capture the whole unified domain model
To reduce duplication, a Shared Kernel is a overlapping subset of the domain model shared by teams
Establish a Customer/Supplier relationship between dependent teams with the former defining integration tests for the latter to improve speed
Conformist are customers that work within a one-sided supplier relationship building on a model that’s given provided there is a rich interface that fulfill their needs.
An Anticorruption layer is a proxy between our clients and a 3rd party (legacy) systems. It’s usually implemented with Facades that our clients interface with which internally use their own adapters with translators to facilitate inter system communication and maintain separation and purity
A separate ways strategy is employed to split an application that has disparate bounded contexts
An open host service wraps a external service as a set of services made available to several of our clients that use it. The protocol is open and avoids a translator per client. Esoteric clients can have a translator to the protocol
Distillation separates the essential parts of a large domain from generic sub domains used is several places. The core distillation is iterative and should be the main focus. Sub domains can use off the shelf solutions, be outsourced, use existing models or an in house solution
References:
This article is part of the system design series where I am summarizing chapters from The System Design Interview: Volume 1 / Volume 2 amongst other related content
