Explain how data is exchanged between digital systems using structured formats such as JSON and XML, application programming interfaces (APIs) and network protocols, and the conditions required for reliable exchange

What this dot point is asking

QCAA wants you to explain how separate digital systems move data between each other reliably. That means understanding structured data formats such as JSON and XML, how APIs let one system request data from another, the network protocols that carry the request, and the conditions (shared format, agreed protocol, validation) that make the exchange work. Unit 4 is about complex data exchange problems, so this is the foundation for IA3.

Structured data formats

Systems built by different developers, in different languages, need a shared text format so each can read the other's data. The two dominant formats are JSON and XML.

JSON (JavaScript Object Notation) is lightweight and the default for modern web APIs. It uses key-value pairs and arrays:

{
  "student_id": 1042,
  "name": "Priya Nguyen",
  "subjects": ["Digital Solutions", "Maths Methods"],
  "enrolled": true
}

XML (Extensible Markup Language) uses nested tags and is more verbose but supports richer metadata:

<student>
  <student_id>1042</student_id>
  <name>Priya Nguyen</name>
  <enrolled>true</enrolled>
</student>

Both are human-readable and language-independent, which is why they are the lingua franca of data exchange. JSON is usually preferred for its smaller size and direct mapping to objects and arrays.

APIs and requests

An API (application programming interface) is the contract that defines how one system asks another for data: which endpoints exist, what parameters they take and what they return. A web API is accessed over HTTP. The common request methods:

• GET: retrieve data.
• POST: send new data to be stored.
• PUT/PATCH: update existing data.
• DELETE: remove data.

Network protocols

A protocol is an agreed set of rules for how data is transmitted. Key ones for this dot point:

• HTTP/HTTPS: carries web API requests; HTTPS adds encryption (see the data security dot points).
• TCP/IP: the underlying transport that splits data into packets, routes them and reassembles them in order.

Both endpoints must speak the same protocol, or the exchange fails before any data is interpreted.

Conditions for reliable exchange

Reliable data exchange requires several conditions to hold simultaneously:

• Agreed format: both systems serialise and parse the same structure (matching JSON schema or XML schema).
• Agreed protocol: both use the same transport and request conventions.
• Validation: the receiver checks incoming data for type, range and completeness before using it.
• Error handling: status codes and timeouts are checked so a failed exchange does not corrupt state.

Missing any one of these turns a working exchange into a silent data-integrity problem.

How this appears in IA3

IA3 is a digital solution centred on a complex data exchange. Markers expect you to choose an appropriate format and protocol, justify the choice against the requirements, validate incoming data, and handle exchange failures gracefully. Show the request, the parsed response and the validation step, and explain why your design exchanges data reliably and securely between the systems involved.