Triples and RDF — AI Tutorials — Subhendu Datta Bhowmik

The RDF Data Model

RDF (Resource Description Framework) is the W3C standard for representing knowledge graph data on the web. It defines a formal model for expressing triples — and by extension, entire knowledge graphs.

In RDF, every piece of information is expressed as a triple:

(Subject) — (Predicate) → (Object)

Each component of the triple is a resource, identified by a URI (Uniform Resource Identifier) or represented as a literal value.

The Three Types of RDF Terms

1. URIs (IRI — Internationalized Resource Identifier)

A URI uniquely identifies a resource. In RDF, URIs look like web URLs:

http://example.org/alice — identifies the person "Alice"
http://xmlns.com/foaf/0.1/knows — the "foaf:knows" predicate
http://www.w3.org/1999/02/22-rdf-syntax-ns#type — the "rdf:type" predicate

Subjects must be URIs (or blank nodes). Predicates must always be URIs. Objects can be URIs or literals.

2. Literals

Literals represent concrete values like strings, numbers, and dates:

"Alice Smith" — a plain string literal
"32"^^xsd:integer — a typed integer literal
"1979-03-14"^^xsd:date — a typed date literal
"Hello"@en — a language-tagged literal (English)

3. Blank Nodes

Blank nodes (bnodes) are anonymous nodes with no URI. They're used to represent complex structures without needing a global identifier:

Useful for intermediate nodes in reification (describing triples with triples)
Identified locally as _:b1, _:b2, etc.

Knowledge graph6 nodes · 5 edges

Nodes

aliceuri
URI: http://example.org/alice
boburi
URI: http://example.org/bob
Acme Corpuri
URI: http://example.org/acme
"Alice Smith"literal
Literal string value
"32"^^xsd:integerliteral
Typed literal: integer 32
"Acme Corporation"literal
Literal string value

Edges

alicefoaf:knowsbob
aliceorg:memberOfacme
alicefoaf:namelit_alice_name
alicefoaf:agelit_age
acmefoaf:namelit_company

An RDF graph showing URI nodes (colored circles) and literal nodes (white rectangles). Predicates are shown as edge labels.

RDF Serialization Formats

RDF triples can be serialized (written to files) in several formats. The most popular are:

Format	Extension	Best for
Turtle	.ttl	Human-readable, most common
JSON-LD	.jsonld	Web APIs, JavaScript apps
N-Triples	.nt	Machine processing, streaming
RDF/XML	.rdf	Legacy systems, verbose

The same data can be expressed in any format — they are all equivalent.

RDF triples

ex:alicefoaf:name"Alice Smith"

Turtle: The Human-Readable Format

Turtle (Terse RDF Triple Language) is the most popular RDF format for writing triples by hand. It uses namespace prefixes to shorten URIs:

The same facts expressed in three RDF formats

@prefix ex:   <http://example.org/> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix org:  <http://www.w3.org/ns/org#> .
@prefix xsd:  <http://www.w3.org/2001/XMLSchema#> .

ex:alice
    a foaf:Person ;
    foaf:name "Alice Smith" ;
    foaf:age  32 ;
    foaf:knows ex:bob ;
    org:memberOf ex:acme .

ex:acme
    a org:Organization ;
    foaf:name "Acme Corp" .

Summary

In this chapter you learned:

RDF is the W3C standard for representing triples — the atomic units of a knowledge graph
RDF terms are URIs (resources), blank nodes (anonymous), or literals (values)
The same graph can be serialized as Turtle, JSON-LD, or N-Triples
Named graphs add a fourth component for provenance and versioning

Next, we'll look at how to define the meaning of your graph's vocabulary using ontologies and the RDFS/OWL languages.

← Knowledge Graphs