JSON-LD

JSON Linked Data is a JSON based payload where

1. Data can be referred/linked from other sources. This will ensure that same data is referred from multiple places. This is the @Id field in JSON-LD.
2. Meanings of data can be central. The field name can be anything, but we just say what it means by using @context. This is where the word machine-understandable comes from.

Why JSON-LD?

It's mainly for global interoperability of data across different systems. For example, multiple organization can share common data definitions in a central place and refer to them in their own data models with any names they wish.

It's coming from a concept called Semantic Web where data is linked across different sources on the web.

JSON-LD and RDF

RDF (Resource Description Framework) is a data model for linked data. Which means, it allows us to represent data as a graph of relationships. RDF represents data as triples: subject, predicate (property/relationship), object. Everything is a 3-tuple.

• Every entity (subject or object) can be identified globally via a URI. (IDs)
• Predicates (properties) are also URIs, giving them precise, machine-readable meaning (Context).

JSON-LD is one of the serializations of RDF. So JSON-LD is a way to represent RDF data model in JSON format.

example mapping

• subject is the @Id in JSON-LD..
• predicate is the field name.
• object is the field value.

NOTE: @type is a special predicate in RDF which is also used in JSON-LD.

Differences to JSON Schema

1. JSON schema is about specific data model with constraints and validations while JSON-LD is about linking data across different sources.
2. JSON uses fixed field names.
3. JSON can't refer to external data
4. HATE-OS in REST APIs only provide URIs to access data, but not the data itself.

different from Hate-OS

In Hate-OS, the clients must use the links to fetch or do other actions on the resource. But in JSON-LD, they URIs just refer to other resources from other sources. The clients can still use the data in the payload directly.

Important Fields in JSON-LD

• @context: defines the meaning of different properties of the object. Usually every field has a context defined. The context can be defined locally or refer to an external source.
• @id: defines the unique identifier of the resource. This refers to any resource, anywhere on the web or local. It's the subject.
• @type: defines the meaning/type of the object itself.