Update Domain-Driven-Design-Implementation-Guide.md

docs/en/Domain-Driven-Design-Implementation-Guide.md

@@ -68,5 +68,12 @@ This section introduces the essential building blocks of the Domain & Applicatio
 * **Value Object**: A [Value Object](Value-Objects.md) is another kind of domain object that is identified by its properties rather than a unique Id. That means two Value Objects with same properties are considered as the same object. Value objects are generally implemented as immutable and mostly are much simpler than the Entities.
 * **Aggregate & Aggregate Root**: An [Aggregate](Entities.md) is a cluster of objects (entities and value objects) bound together by an **Aggregate Root** object. The Aggregate Root is a specific type of an entity with some additional responsibilities.
 * **Repository**: A [Repository](Repositories.md) is a collection-like interface that is used by the Domain and Application Layers to access to the data persistence system (the database). It hides the complexity of the DBMS from the business code.
+* **Domain Service**: A [Domain Service](Domain-Services.md) is a stateless service that implements core business rules of the domain. It is useful to implement domain logic that depends on multiple aggregate (entity) type or some external services.
+* **Specification**: A [Specification](Specifications.md) is used to define named, reusable and combinable filters for entities and other business objects.
+* **Domain Event**: A [Domain Event](Event-Bus.md) is a way of informing other services in a loosely coupled manner, when a domain specific event occurs.
 
-#### Application Layer Building Blocks
+#### Application Layer Building Blocks
+
+* **Application Service**: An [Application Service](Application-Services.md) is a stateless service that implements use cases of the application. An application service typically gets and returns DTOs. It is used by the Presentation Layer. It uses and coordinates the domain objects to implement the use cases. A use case is typically considered as a Unit Of Work.
+* **Data Transfer Object (DTO)**: A [DTO](Data-Transfer-Objects.md) is a simple object without any business logic that is used to transfer state (data) between the Application and Presentation Layers.
+* **Unit of Work (UOW)**: A [Unit of Work](Unit-Of-Work.md) is an atomic work that should be done as a transaction unit. All the operations inside a UOW should be committed on success or rolled back on a failure.