Aggregate root is a meaningful object in the domain. It can be viewed as a write boundary for entities and value objects that will maintain write consistency.

Usually it represents a single table, but can span several tables and can be used like document or similar data structure. Since every aggregate is also an entity, it has a unique identification represented by its URI.

DSL example:

module Todo {
  aggregate Task {
    Timestamp  startedAt;
    Timestamp? finishedAt;
    Int?       priority;
    Seq<Note>  notes;
  }

  value Note {
    Date   entered;
    String remark;
  }
}