Item:OSWf1df064239044b8fa3c968339fb93344

JSON Tutorial [OSWf1df064239044b8fa3c968339fb93344]
ID	OSWf1df064239044b8fa3c968339fb93344
UUID	f1df0642-3904-4b8f-a3c9-68339fb93344
Label	JSON Tutorial
Machine compatible name	JsonTutorial
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Description

Covers basics about JSON-Documents

Item
Type(s)/Category(s)	Tutorial

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Article

Tutorial
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Prerequisites (optional)
Follow-up (recommended)	JSON-SCHEMA Tutorial JSON-LD Tutorial

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JSON Documents: Basics

What is a JSON?

• A JSON itself is a JSON object, marked by [1]

{}

JSON Documents: Key-Value-Pairs

• A JSON object defines key(word):value pairs.
• Keys are formatted as strings, marked by quotation marks ("").

{
    "key": "value"
}

JSON Documents: Data types

• The key is always a string
• The value can be a string, a number, a boolean or null
• Additional data types are only possible by referencing them as external resources

{
    "key": "value",
    "string": "any string value",
    "number": 1.0,
    "bool": true,
    "empty": null,
    "image": "https://my.cloud/image-1.png"
}

JSON Documents: Subobjects

• The value can also be a JSON document (object) itself
• A nested object can have the same key-value pairs as the root document
• There is no limit in the nesting depth

{
    "key": "value",
    "string": "any string value",
    "number": 1.0,
    "bool": true,
    "empty": null,
    "object": {
        "has": "it's own key-value-pairs"
    }
}

JSON Documents: Arrays

• The value can also be an array (list)
• An array can contain any element, including objects and nested arrays

{
    "key": "value",
    "string": "any string value",
    "number": 1.0,
    "bool": true,
    "empty": null,
    "object": {
        "has": "it's own key-value-pairs"
    },
    "array": [
        "a list", 
        {"of": "any"}, 
        ["item1", 1.0, true]
    ]
}

JSON Documents: Pointer

Pointer allow reference to

• An object within the JSON document

{
    "firstname": "Susan",
    "surname": "Birch",
    "kids": ["Anne", "Tom"],
    "emergency_contact": {
        "$ref": "#/kids/0"
    }    
}

Syntax [2]:

# - the whole document = self-reference

#/kids - the value of the key "kids"

#/kids/0 - the first item within the array "kids"

JSON Documents: Reference

References allow reference to

• An external JSON document
• Combined with a pointer: An object within the external JSON document

{
    "firstname": "Susan",
    "surname": "Birch",
    "partner": {
        "$ref": "http://www.personaldata.com/walter.birch.json"
    },
    "partner_firstname": {
        "$ref": "http://www.personaldata.com/walter.birch.json#firstname"
    }
}

Specification: [3]

JSON Documents: Path

Paths allow query / filter values within a JSON document

{
  "store": {
    "book": [
      { "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ]
  }
}

• $.store.book[*].price => [8.95, 22.99]
• $.store.book[?(@.title == 'The Lord of the Rings')].price => 22.99

Specification: [4]

Conceptually also available as AWS S3 Select[5] and Postgres JSONB [6]

JSON vs. YAML

YAML version 1.2 is a superset of JSON with a simplified syntax

JSON (more machine-friendly)

{
  "store": {
    "book": [
      { "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ]
  }
}

YAML (more human-friendly)

# comments are allowed
store:
  book:
  - author: Nigel Rees
    title: Sayings of the Century
    price: 8.95
  - author: J. R. R. Tolkien
    title: The Lord of the Rings
    isbn: 0-395-19395-8 
    price: 22.99

JSON Documents: Next

• JSON-SCHEMA Tutorial Slideshow
• JSON-LD Tutorial Slideshow

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