In this talk, learn how you can use JSON Schema to write a specification language. You will learn about what Domain Specific Languages are, how the WAML web automation language was developed using JSON Schema, and the far-reaching applications of JSON Schema in other domains such as Headless CMSes.

2. Writing Domain Specific Languages
with JSON Schema
Yos Riady
yos.io
bit.ly/2JbMTrn

3. Weak types in JSON
What is JSON Schema?
Introduction Schema Uses DSL Conclusion
JSON Schema use
cases
Summary and further
learning
Writing a DSL with
JSON Schema

5. JSON is weakly typed
{
“userName”: “Yos”,
“favouriteNumber”: 42,
“interests”: [“programming”, “swimming”]
}

7. message Person {
required string user_name = 1
optional int64 favourite_number = 2
repeated string interests = 3
}
Protocol Buffers are strongly typed

9. How can we validate
JSON data with types?

10. Enter JSON Schema
{
“userName”: { “type”: “string” },
“favouriteNumber”: { “type”: “integer” },
“interests”: { “type”: “array”, “items”: { “type”: “string”} }
}

11. JSON Schema helps you validate
JSON data.

12. jsonschemalint.com

13. JSON Schema 101
{
"type": "string"
}
Valid Invalid
“foo” 123
false

14. JSON Schema Basic Types
● string
● Numeric types
● object
● array
● boolean
● null

15. {
"type": "object",
"properties": {
"userName": {
"type": "string"
}
},
"required": ["userName"],
"additionalProperties": false,
}
JSON Schema 101 Valid Invalid
{
“userName”:
“foo”
}
{
“userName”: 1
}
{
“name”: “foo”
}
{}

16. JSON Schema 101
Invalid Validation Message
{
“userName”: 1
}
Field .userName should be a string
{
“name”: “foo”
}
Should NOT have additional properties
{} Should have required property ‘userName’

17. Additional JSON Schema Validations
{
"type": "number",
"minimum": 0,
"maximum": 100,
"exclusiveMaximum": true
}
{
"type": "string",
"pattern": "^(([0-9]{3}))?[0-9]{3}-[0-9]{4}$"
}

18. Combining JSON Schemas
● AnyOf
● AllOf
● OneOf
● not
{
"anyOf": [
{ "type": "string" },
{ "type": "number" }
]
}

19. Structuring Complex Schemas
{
"definitions": {
"person": { ... }
},
"type": "object",
"properties": {
"user": { "$ref": "#/definitions/person" }
}
}

21. jsonschemalint.com

22. Use Cases for JSON Schema
● Message / data validation
○ Object Relational Mappers (ORMs)
● Schemaless objects in Web Applications
● Content Management in Headless CMSes
● Writing Specification Languages
○ OpenAPI / Swagger
○ AWS States Language
○ WAML

23. Hapi.js object validation

24. Dynamic forms

25. Content Modeling in Headless CMSes

26. Content Modeling in Headless CMSes

27. Writing Specification Languages

28. Weak types in JSON
What is JSON Schema?
Introduction Schema Uses DSL Conclusion
JSON Schema use
cases
Summary and further
learning
Writing a DSL with
JSON Schema

29. Writing a DSL with JSON Schema

30. Domain Specific Languages
● Computer language specialized to a particular application domain
○ In contrast to General Purpose Languages (GPLs)

31. OpenAPI / Swagger

32. Web Automation Markup Language (waml.io)

33. waml.io/editor

34. Writing a DSL with JSON Schema
"waml": {
"description": "WAML Specification semantic version number.",
"type": "string",
"pattern": "^([0-9]{1,}.[0-9]{1,}.[0-9]{1,})$",
"enum": ["0.1.0"]
}

35. Writing a DSL with JSON Schema
"steps": {
"type": "array",
"minItems": 1,
"items": {
"$ref": "#/definitions/Step"
}
}

36. Writing a DSL with JSON Schema
"Step": {
"type": "object",
"description": "A step represents a single user interaction.",
"oneOf": [
{
"$ref": "#/definitions/VisitStep"
},
{
"$ref": "#/definitions/ClickStep"
}
]
}

37. "ClickStep": {
"type": "object",
"properties": {
"click": {
"oneOf": [
{
"type": "string"
},
{
"type": "object",
"properties": {
"selector": { "type": "string" },
"index": { "type": "integer", "minimum": 0 }
}
}
]
},
},
}

38. github.com/waml-lang/waml

39. Weak types in JSON
What is JSON Schema?
Introduction Schema Uses DSL Conclusion
JSON Schema use
cases
Summary and further
learning
Writing a DSL with
JSON Schema

40. ● JSON is weakly typed
● JSON Schema
○ What is JSON Schema?
○ JSON validation with JSON Schema
○ Use cases
● Domain Specific Languages
○ What are DSLs?
○ Writing a DSL with JSON Schema
In Closing

42. Writing Domain Specific Languages
with JSON Schema
Yos Riady
yos.io
bit.ly/2JbMTrn

43. Q&A