JSON and structured data

Structured data has an organised shape

Structured data follows a predictable organisation so programs can locate, filter and transform values. JSON (JavaScript Object Notation) is a text format commonly used to exchange data between systems and applications.

{
  "event_id": 42,
  "name": "Robotics showcase",
  "cancelled": false,
  "tags": ["technology", "community"]
}

Objects, arrays, keys and values

Read the structure

{
  "station": "North",
  "readings": [18, 21, 19],
  "active": true
}

Recognise the object, its three keys, the array and each value's type.

JSON value types

• String: text inside double quotes, e.g. "open".
• Number: an integer or decimal without quotes, e.g. 27 or 3.5.
• Boolean: lowercase true or false.
• Null: lowercase null, meaning no value is supplied.
• Object: nested named values inside braces.
• Array: an ordered collection inside square brackets.

A quoted number such as "27" is a string. Its appearance does not change its type.

Choose suitable types

Determine a suitable JSON type for an attendee name, ticket price, checked-in state, optional accessibility note and list of session IDs.

Valid JSON syntax

• Keys and string values use double quotes.
• A colon separates a key from its value.
• A comma separates pairs or array items, but no comma follows the final item.
• Braces and brackets must be balanced and correctly nested.
• Comments and undefined are not part of standard JSON.

Repair malformed JSON

{
  event_id: 7,
  "title": 'Night market',
  "open": True,
  "stalls": [12, 15,],
}

Analyse the data and rewrite it as valid JSON.

{
  "event_id": 7,
  "title": "Night market",
  "open": true,
  "stalls": [12, 15]
}

Nested objects and arrays

{
  "venue": {
    "name": "River Hall",
    "address": {"suburb": "West End", "postcode": "4101"}
  },
  "sessions": [
    {"session_id": 1, "places": 0},
    {"session_id": 2, "places": 8}
  ]
}

Read a path one container at a time. The postcode path is venue → address → postcode. The second session's places path is sessions → item 2 → places.

Trace the paths

Determine the suburb, the first session ID and the number of places in the second session.

Collections of records

An API response often wraps an array of consistently shaped objects.

{
  "results": [
    {"id": 101, "suburb": "Nundah", "status": "open"},
    {"id": 102, "suburb": "Nundah", "status": "closed"},
    {"id": 103, "suburb": "Milton", "status": "open"}
  ],
  "result_count": 3
}

Consistency matters. The same concept should normally use the same key name and compatible type in every record.

Filter the records

Develop language-independent pseudocode that outputs the ID of each open Nundah record.

FOR EACH record IN data["results"] DO
    IF record["suburb"] = "Nundah" AND record["status"] = "open" THEN
        OUTPUT record["id"]
    ENDIF
ENDFOR

Parse, validate, transform and serialise

1. Receive: obtain JSON text from a file, message or API.
2. Parse: convert the text into an internal object or collection.
3. Validate: check required keys, types, formats and allowed values.
4. Transform: filter, calculate, rename, group or combine data.
5. Serialise: convert internal data back into JSON text for exchange.

Valid syntax does not guarantee valid data. {"places": -9} is syntactically valid but may break a rule that places cannot be negative.

Validate before use

A booking requires booking_id as a positive integer, email as a non-empty string and confirmed as a Boolean.

{"booking_id": "24", "email": "", "confirmed": "false"}

Analyse the record against the rules.

Design data for exchange

Choose keys that are meaningful, consistent and unambiguous. Avoid mixing display labels with stable identifiers.

• Use student_id to identify a student reliably, even if their displayed name changes.
• Choose one naming convention, such as snake_case, and apply it consistently.
• Represent repeated items as an array rather than numbered keys such as item1 and item2.
• Do not include sensitive fields unless the receiver needs them.
• Document units and date formats in the data specification.

Explain a design choice

Explain why an array is more suitable than the keys tag1, tag2 and tag3 for storing an unknown number of tags.

Independent practice: community workshops

{
  "generated_at": "2026-08-05T09:30:00+10:00",
  "workshops": [
    {
      "workshop_id": 11,
      "title": "Bike repair",
      "venue": {"name": "Shed A", "accessible": true},
      "capacity": 16,
      "booked": 16,
      "tags": ["practical", "transport"]
    },
    {
      "workshop_id": 12,
      "title": "Native gardens",
      "venue": {"name": "Courtyard", "accessible": false},
      "capacity": 20,
      "booked": 13,
      "tags": ["outdoors"]
    }
  ]
}

1. Describe the outer structure and the structure of one workshop.
2. Determine the path to the second workshop's accessibility value.
3. Develop pseudocode that outputs the titles of accessible workshops with at least one place remaining.
4. Explain why workshop_id should be retained when sending a selected workshop back to the server.