0. Domain Driven Design and Event Sourcing with RIM

1. Introduction
RIMResistance is Futile, you Will be Assimilated!

2. Introduction DDD and Event Sourcing George de la Torre
Developer of custom clinical apps
For a long time
Discovered RIM a long time ago…
Oleg Sitalo (silent partner)
Developer of custom clinical apps
For a long time together
Believes in RIM, at occasions…

3. Agenda DDD and Event Sourcing Google will find heaps of stuff on this
Will focus on the RIM stuff
Great resources for DDD/ES
Implementing Doman-Driven Design
Vaughn Vernon
Domain Driven Design (the Blue Book)
Eric Evans

4. Domain Driven Design DDD and Event Sourcing Object Oriented Model
Business needs & language captured
HL7 v3 RIM benefits
Design done! – the hardest part
Standard – open & shared to all
Deep insights into domain knowledge
Integration of domains built in (No barriers!)
Reuse logic across clinical domains

5. Domain Model Blueprint for all Aggregates
HL7 V3 RIM

6. Supporting Domains External Services
Vocabulary
Bounded Contexts

7. Supporting Domains External Services
Anti Corruption Layer
Other systems or Big Ball of Mud…
Business Process and Rules Engines
Point: This layer keeps RIM pure!

8. Event Sourcing DDD and Event Sourcing
Only the Aggregate (D-MIM) is persisted
The command is saved (Behavior)
Aggregates publishes the events
Command Query Responsibility Segregation (CQRS)
Command (Transaction) Model
Query Model

9. Patient Dashboard Example Use Case
Schedule a patient visit
Find Patient (Query Model)
View Calendar (Query Model)
Patient assigned time slot (Command)
CreateAppointmentCommand(data) executes
Scheduling aggregate is created from data
The created aggregate is appended
Publishes event to update Query Model

10. Scheduling Aggregate Example

11. Scheduling Aggregate CMET (PAT) is the Root

12. Considerations Scheduling Aggregate Entity is usually the Root
No cloning, only class codes
Aggregates varies with the RIM set
Act may be the Root (Strategy)
Reference others Aggregates (Observations)
Act Mood partitioning
PHI segregation requirement (Query model too)
Performance

13. Considerations continued…
Scheduling Aggregate
Considerations continued…
Serialized, XML, JSON, etc…
Relational Database (SQL)
Cache based systems
File systems
NoSQL
Natural for event stores
Easier to query Aggregates if needed
Aggregates loaded for logic on command

14. Scheduling Aggregate Appended
CreateAppointmentCommand(data)
Event Store ID
Name
Version
Data 1
Schedule
1.2 2 3

15. Scheduling Aggregate Publishes Events
AppointmentCreatedEvent(data) {
UpdateDatabaseView() }
Query model
MRN
First
Last
DOB
Phone
Start
End
Note

16. Scheduling Aggregate Publishes Events
AppointmentCreatedEvent() {
CreateAdmissionMessage() }
HL7 2.x
MSH|^~\&|ADT1|MCM|LABADT|MCM| |SECURITY|ADT^A01|MSG00001-|P|2.3
EVN|A01|
PID|||PATID1234^5^M11||JONES^WILLIAM^A^III|| |M-||C|1200 N ELM
STREET^^GREENSBORO^NC^ |GL|(91-9) |(919)271-
3434||S||PATID ^2^M10| | ^NC

17. Scheduling Aggregate Publishes Events
AppointmentCreatedEvent() {
UpdateDataMart() }

18. Patient Dashboard Example Two Separate Models (CQRS)
Domain (Transaction) Model
Complex structure (RIM)
Aggregates are only created from RIM
Aggregates are appended (Write Only)
Query Model
Simplified model structure (SQL)
Multiple models created as needed
Model optimized for querying (Read Only)

19. Simple Component Design CQRS
Web
Dashboard
View Model
Aggregate Services
App Services
Publishes to
Commands
Query
Events
SQL