The philosophy of ubiquitous language

So, you decided to try Domain-Driven Design (DDD). You start modeling the domain using the language spoken by your domain experts. All goes well… until you discover ambiguities. What do you do now? How do you keep your model clean while still respecting the ubiquitous language?

Well, it depends. It depends on your philosophical presuppositions, to be precise. The way you think language works will to a large extent determine your course of action. So instead of looking to DDD creator Eric Evans for the answer, I propose looking in an entirely different direction: the philosophy of Ludwig Wittgenstein (1889 - 1951). Wittgenstein’s revolutionary insights into the nature of meaning provide some excellent pointers for diagnosing the source of your modeling problem – not to mention showing you the way out!

At the end of this session, you’ll have gained a clearer understanding of the way language works and how you can use this knowledge to build better software. Whether you’re new to DDD or a seasoned veteran, this talk is sure to provide you with a new outlook on your development activities.

Transcript

1. The philosophy of ubiquitous language Karl van Heijster www.karlvanheijster.com
2. Domain-Driven Design & Ludwig Wittgenstein Karl van Heijster www.karlvanheijster.com
4. Software craftsman Philosopher DDD amateur www.karlvanheijster.com Karl van Heijster
12. Object Module Module Module Module
13. Product - Id - Name - Description - Price - Cost - Quantity Catalog Sales Purchasing Warehouse
14. Product - Id - Name - Description - Price - Cost - Quantity Catalog Sales Purchasing Warehouse
15. Product - Id - Name - Description - Price - Cost - Quantity Catalog Sales Purchasing Warehouse
16. Product - Id - Name - Description - Price - Cost - Quantity Catalog Sales Purchasing Warehouse
17. Product - Id - Name - Description - Price - Cost - Quantity Catalog Sales Purchasing Warehouse
22. SalesProduct - Id - Price Catalog Sales Purchasing Warehouse PurchasingProduct - Id - Cost WarehouseProduct - Id - Quantity CatalogProduct - Id - Name - Description
28. “The cat is on the mat”
29. “The cat is on the mat”
30. “The cat is on the mat”
31. “The cat is on the mat”
33. “The cat is on the mat” true
34. “The cat is on the mat” false
37. aRb cat.IsOn(mat);
38. “The present king of France is bald”
39. aRb
40. aRb presentKingOfFrance.IsBald
41. ∃x((Kx ∧ ∀y(Ky → y = x)) ∧ Bx) x is not null && x.IsKing && y.All(y => y.IsKing ? y == x : true) && x.IsBald;
44. SalesProduct - Id - Price Catalog Sales Purchasing Warehouse PurchasingProduct - Id - Cost WarehouseProduct - Id - Quantity CatalogProduct - Id - Name - Description
60. “The cat is on the mat” • Help me find my cat • Describe the contents of a picture • Use coded language, “The eagle has landed” • Rhyming
66. SalesProduct - Id - Price Catalog Sales Purchasing Warehouse PurchasingProduct - Id - Cost WarehouseProduct - Id - Quantity CatalogProduct - Id - Name - Description
67. Product - Id - Price Catalog Sales Purchasing Warehouse Product - Id - Cost Product - Id - Quantity Product - Id - Name - Description
68. Product - Id - Price Catalog Sales Purchasing Warehouse Product - Id - Cost Product - Id - Quantity Product - Id - Name - Description
76. The philosophy of ubiquitous language Karl van Heijster www.karlvanheijster.com