Work shop eventstorming
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An introduction to EventStorming technique and its implication in software development
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Work shop eventstorming
- 1. Event Storming PROCESS, STICKES & EVENTS Francesco Garavaglia 01/2016
- 2. Agenda The problem The solution: Event storming Summary
- 3. 3 The Problem The Problem 0 0,2 0,4 0,6 0,8 1 1,2 1,00 2,00 3,00 4,00 5,00 6,00 7,00 8,00 9,00 10,00 Complexity Time elapsed Changing Cost Green Field illusion Maintainence I cannot do this Refactoring from scratch
- 4. How to gather requirements from many different departments/speci alists? 4 Department C Department E Department A Department D Department B
- 6. 6 Or design by committee? The Problem
- 7. 7 Event Storming Event Storming is a fun way of bringing developers and business experts together and drive your analysis from the outside and quickly explore complex business domains in hours instead of days/weeks. Event Storming (or Model storming) is a way of starting your analysis from the outside and quickly explore complex business domains. Invented by Alberto Brandolini See http://ziobrando.blogspot.dk/2013/11/introducing- event-storming.html The Problem
- 8. Much requirements gathering still follow in the steps of structural or classic OO design WE WRITE USE CASES/STORIES AND AFTERWARDS LOOK FOR NOUNS AND VERBS 8
- 9. 9 Usually we start with a simple model The Problem
- 10. 10 And as time goes by… The Problem
- 11. 11 It gets more complicated The Problem
- 12. 12 And finally we drown The Problem
- 13. We end up with One Domain Model to Rule them All CAN’T WE AVOID CEREMONIAL MODELING? SOMETHING EASIER, FASTER AND BETTER? 13
- 14. 14 Event Storming All togher into the same room Unlimited modelling surface Invite the right People Those who bring the questions Those who know the answers (not all of them) Value is in the interaction between people: miss one and you’ll miss n-1 interactions Refine the model step-by-step The Solution: ES
- 15. 15 Hack the space There is no perfect room for a event storming Hacking the space is up to you Unlimited modelling space: can’t tell a problem size before exploring it Table creates the wrong phisical space position are fixed, no emerging alliances posture is far from optimal too easy to switch on laptops or other distractions No body language to observe The Solution: ES
- 17. 17 How to run EventStorming session Explore the domain starting from Domain/Business Simple semantic and notation Represent the state transitions Gives us precision Easy to grasp by everybody in the room Place them along a timeline to visualize the process An event might be the predecessor or the follower of another one The Solution: ES
- 18. 18 An Event message is non-prescriptive of what should happen in other services. It leaves this open to the recipients, so that they themselves determine what to do based on occurrence of the event. Events always carry a name in its past-tense form: OrderWasAccepted, OrderHasShipped, CustomerWasReimbursed Other qualities Immutable, i.e. content cannot be changed Always carries the ID of the Business Object it relates to An event can and will typically will be published to multiple consumers. The publisher of the event does not know who the recipients are And it doesn’t know what the recipients intend to do with the event “An Event describes something that HAS happened” What is an Event? The Solution: ES
- 19. 19 User Action model it as a Command External system Time Other Domain Events Documents External Time Command Role Event Event Document What does it cause Domain Events? The Solution: ES
- 20. 20 Define a language… A physical model provides a safe support for spotting critical areas in your business process It’s not like that The Solution: ES
- 21. 21 ..Along the time line Enforce narratives: People like telling Stories, not just filling diagrams or template Encourage experts to tell a story Look for concrete examples look for edge cases, they fit perfectly in a narrative and they should fit into your model too Eventually turn them into tests The Solution: ES
- 22. 22 Or reverse narrative Use Time line in a reverse mode: What was the path that led us here? What needs to happen before, so that this event can happen too? The Solution: ES
- 23. 23 A Command message is prescriptive of what should happen. This is a stronger form of coupling than Event and Document messages. A Command’s primary goal is to capture USER INTENT A Command supports a single usecase and targets a single Business Object Commands always carry a name in its imperative form: CreateOrder, ShipOrder, CancelOrder, ReimburseCustomer, etc. Other qualities Immutable, i.e. content cannot be changed Always carries the ID of the Business Object that it relates to A command can only be handled by ONE service The Operations that consume Commands don’t return values – but can throw exceptions Commands mutate Business Object state which results in one or more Events being published “A command describes a Task that you want someone else to carry out for you and the recipient can reject the Command” Events are often the side effect of Commands The Solution: ES
- 24. 24 Commands & Events Receives a Command Asynchronousl y Publishes multiple Events asynchronously The Solution: ES
- 25. 25 Entering the process manager Process managers are the home of reactive behaviour in the systems «Whanaver» is the most common word here Whenever we receive an invoice we schedule a payment Whenever we receive a Bs.we try to reconcile it Suppler invoice receiver Bank Statement Received Schedule Payment Reconcile Operation The Solution: ES
- 26. 26 Using Business Events to drive Business Processes Sales Service Shipping Billing Sales Customers MessageChannel Online Ordering System Web Shop (Composite UI) Billing Service Shipping Service Order Accepted Event AcceptOrde r Command The sales fulfillment processing can now begin… The Solution: ES
- 27. 27 Not all the results are visible The model on the paper roll is huge and tangible but more value is created along the way Event Storming More often than not, old problems find a solution during the workshop The Solution: ES
- 28. 28 Not all the results are visible Conflicts and potential overlappings are highlighted Can finally see the Big Picture Conversations can finally Happen And ideas are popping out The Solution: ES
- 29. 29 Explore Aggregates Outside In An Aggregate receives Commands and decides to execute them or reject them If the Aggregate executes a Command it will produce one or more Domain Events as a result Exploring….. The Solution: ES
- 30. 30 Invoice InvoiceLine * Account * What: • Cluster coherent Entities and Value Objects, with complex associations into Aggregates with well defined boundaries. • Choose one entity to be root and control access to objects inside the boundary through the root. • External objects hold references to the root • Aggregates only refer to other aggregates by identity (their id) Motivation: Control invariants and consistency through the aggregate root. Enables: Loading schemes, coarse grained locking and… Ensuring consistency & transactional boundaries for Distributed scenarios Root ….Aggregates The Solution: ES
- 31. 31 Explore Sub domains Different areas of responsibility map pretty well to different subdomains or portions of the pork Explore Bounded Contexts During the discussion, some conflict areas with regards to different interpretations of terms might emerge Draw boundaries between the multiple consistent models that will coexist in your domain 31 … And sub-domains The Solution: ES
- 32. 32 Conceptual CQRS Users decide actions according to the real world experience (things they know which are not in the system) and read Model Humans decide according to different sets of info (ex: faces, pictures, surnames, ecc) The model of anything: CQRS The Solution: ES
- 33. 33 Summary: Event Storming Legend: User Action modeled as a Command External system Time Domain Events Documents IT Operations (Gateway) Aggregate Read Model External Time Comma nd Role Event Event Docume nt IT Ops Read Model Aggregate Summary
- 34. 34 Event Storming is Powerful come up with a comprehensive model of a complete business flow in hours instead of weeks. Engaging: bring people with the questions and people who know the answer in the same room and to build a model together Efficient the resulting model is perfectly aligned with Event Sourcing and EDA, and allows for a quick determination of Bounded Context and Aggregate boundaries and thereby also Service boundaries Easy the notation is ultra-simple. No complex UML Fun Eventstorming workshops and fun, people are energized and deliver more than they expected. The right questions arise, and the atmosphere is the right one. Summary