diff --git a/lib/booking.rb b/lib/booking.rb
index 2821d29..d011b65 100644
--- a/lib/booking.rb
+++ b/lib/booking.rb
@@ -1,15 +1,9 @@
 module Booking
-  Event = Data.define(:data, :event_type) do
-    def initialize(data: Hash.new)
-      super(data: data, event_type: self.class.name)
-    end
-  end
+  ScheduleReleased = Data.define(:scheduled_at, :duration)
+  ScheduleReserved = Data.define(:scheduled_at, :duration)
 
-  ScheduleReleased = Class.new(Event)
-  ScheduleReserved = Class.new(Event)
-
-  AppointmentProposed = Class.new(Event)
-  AppointmentAccepted = Class.new(Event)
-  AppointmentRejected = Class.new(Event)
-  AppointmentCancelled = Class.new(Event)
+  AppointmentProposed = Data.define(:id, :proposed_at)
+  AppointmentAccepted = Data.define(:id, :accepted_at)
+  AppointmentRejected = Data.define(:id, :rejected_at)
+  AppointmentCancelled = Data.define(:id, :cancelled_at)
 end
diff --git a/lib/booking/appointment.rb b/lib/booking/appointment.rb
index fe79988..d9c0f8e 100644
--- a/lib/booking/appointment.rb
+++ b/lib/booking/appointment.rb
@@ -11,24 +11,24 @@ def initialize(id, clock:)
     def propose
       invalid_state unless @state.initial?
       @state.to_proposed
-      AppointmentProposed.new(data: { id: @id, proposed_at: @clock.call })
+      AppointmentProposed.new(id: @id, proposed_at: @clock.call)
     end
 
     def accept
       invalid_state unless @state.proposed?
       @state.to_accepted
-      AppointmentAccepted.new(data: { id: @id, accepted_at: @clock.call })
+      AppointmentAccepted.new(id: @id, accepted_at: @clock.call)
     end
 
     def reject
       invalid_state unless @state.proposed?
       @state.to_rejected
-      AppointmentRejected.new(data: { id: @id, rejected_at: @clock.call })
+      AppointmentRejected.new(id: @id, rejected_at: @clock.call)
     end
 
     def cancel
       invalid_state unless @state.accepted? || @state.proposed?
-      AppointmentCancelled.new(data: { id: @id, cancelled_at: @clock.call })
+      AppointmentCancelled.new(id: @id, cancelled_at: @clock.call)
     end
 
     private
diff --git a/lib/booking/day_schedule.rb b/lib/booking/day_schedule.rb
index 60af62a..0814ed3 100644
--- a/lib/booking/day_schedule.rb
+++ b/lib/booking/day_schedule.rb
@@ -26,19 +26,15 @@ def release(time_range)
 
     def visit_scheduled(time_range)
       ScheduleReserved.new(
-        data: {
-          scheduled_at: time_range.first,
-          duration: time_range.last - time_range.first
-        }
+        scheduled_at: time_range.first,
+        duration: time_range.last - time_range.first
       )
     end
 
     def visit_released(time_range)
       ScheduleReleased.new(
-        data: {
-          scheduled_at: time_range.first,
-          duration: time_range.last - time_range.first
-        }
+        scheduled_at: time_range.first,
+        duration: time_range.last - time_range.first
       )
     end
 
diff --git a/test/lib/booking/appointment_test.rb b/test/lib/booking/appointment_test.rb
index 5886b01..05bd19c 100644
--- a/test/lib/booking/appointment_test.rb
+++ b/test/lib/booking/appointment_test.rb
@@ -6,7 +6,7 @@ class AppointmentTest < ActiveSupport::TestCase
 
     test "propose" do
       appointment = new_appointment
-      assert_event appointment_proposed, appointment.propose
+      assert_domain_event appointment_proposed, appointment.propose
     end
 
     test "cannot propose twice" do
@@ -20,7 +20,7 @@ class AppointmentTest < ActiveSupport::TestCase
       appointment = new_appointment
       appointment.propose
 
-      assert_event appointment_accepted, appointment.accept
+      assert_domain_event appointment_accepted, appointment.accept
     end
 
     test "cannot accept without proposal" do
@@ -40,7 +40,7 @@ class AppointmentTest < ActiveSupport::TestCase
       appointment = new_appointment
       appointment.propose
 
-      assert_event appointment_rejected, appointment.reject
+      assert_domain_event appointment_rejected, appointment.reject
     end
 
     test "cannot reject without proposal" do
@@ -92,7 +92,7 @@ class AppointmentTest < ActiveSupport::TestCase
       appointment = new_appointment
       appointment.propose
 
-      assert_event appointment_cancelled, appointment.cancel
+      assert_domain_event appointment_cancelled, appointment.cancel
     end
 
     test "cancel accepted appointment" do
@@ -100,7 +100,7 @@ class AppointmentTest < ActiveSupport::TestCase
       appointment.propose
       appointment.accept
 
-      assert_event appointment_cancelled, appointment.cancel
+      assert_domain_event appointment_cancelled, appointment.cancel
     end
 
     test "cannot cancel rejected appointment" do
@@ -136,37 +136,29 @@ def new_appointment
 
     def appointment_proposed
       AppointmentProposed.new(
-        data: {
-          id: appointment_id,
-          proposed_at: current_time
-        }
+        id: appointment_id,
+        proposed_at: current_time
       )
     end
 
     def appointment_accepted
       AppointmentAccepted.new(
-        data: {
-          id: appointment_id,
-          accepted_at: current_time
-        }
+        id: appointment_id,
+        accepted_at: current_time
       )
     end
 
     def appointment_rejected
       AppointmentRejected.new(
-        data: {
-          id: appointment_id,
-          rejected_at: current_time
-        }
+        id: appointment_id,
+        rejected_at: current_time
       )
     end
 
     def appointment_cancelled
       AppointmentCancelled.new(
-        data: {
-          id: appointment_id,
-          cancelled_at: current_time
-        }
+        id: appointment_id,
+        cancelled_at: current_time
       )
     end
   end
diff --git a/test/lib/booking/day_schedule_test.rb b/test/lib/booking/day_schedule_test.rb
index c1a4d75..8521b2c 100644
--- a/test/lib/booking/day_schedule_test.rb
+++ b/test/lib/booking/day_schedule_test.rb
@@ -7,7 +7,7 @@ class DayScheduleTest < ActiveSupport::TestCase
     test "happy path" do
       day_schedule = DaySchedule.new(open_hours)
 
-      assert_event visit_scheduled(slot), day_schedule.reserve(slot)
+      assert_domain_event visit_scheduled(slot), day_schedule.reserve(slot)
     end
 
     test "cannot reserve same slot twice" do
@@ -41,7 +41,7 @@ class DayScheduleTest < ActiveSupport::TestCase
       day_schedule = DaySchedule.new(open_hours)
       day_schedule.reserve(rush_by(1.hour, slot))
 
-      assert_event visit_scheduled(slot), day_schedule.reserve(slot)
+      assert_domain_event visit_scheduled(slot), day_schedule.reserve(slot)
     end
 
     test "cannot reserve outside of open hours" do
@@ -54,7 +54,7 @@ class DayScheduleTest < ActiveSupport::TestCase
       day_schedule = DaySchedule.new(open_hours)
       day_schedule.reserve(slot)
 
-      assert_event visit_released(slot), day_schedule.release(slot)
+      assert_domain_event visit_released(slot), day_schedule.release(slot)
     end
 
     test "released slot can be taken again" do
@@ -91,19 +91,15 @@ def rush_by(seconds, slot)
 
     def visit_scheduled(time_range)
       ScheduleReserved.new(
-        data: {
-          scheduled_at: time_range.first,
-          duration: time_range.last - time_range.first
-        }
+        scheduled_at: time_range.first,
+        duration: time_range.last - time_range.first
       )
     end
 
     def visit_released(time_range)
       ScheduleReleased.new(
-        data: {
-          scheduled_at: time_range.first,
-          duration: time_range.last - time_range.first
-        }
+        scheduled_at: time_range.first,
+        duration: time_range.last - time_range.first
       )
     end
   end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index f7846e4..cd151d7 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -13,9 +13,9 @@ class TestCase
 
     # Add more helper methods to be used by all tests here...
 
-    def assert_event(expected, actual)
-      assert_equal expected.event_type, actual.event_type
-      assert_equal expected.data, actual.data
+    def assert_domain_event(expected, actual)
+      assert_equal expected.class, actual.class
+      assert_equal expected.deconstruct_keys(nil), actual.deconstruct_keys(nil)
     end
   end
 end