Introduction to RDF and Basic Modeling

Last updated on 2025-04-08 | Edit this page

Overview

Questions

  • What is RDF, and why is it used in Linked Open Data?
  • How does RDF structure information?
  • How can we represent real-world relationships using RDF?

Objectives

  • Explain the purpose and structure of RDF.
  • Model basic relationships using RDF.
  • Explain limitations of n-triples.

As we have already learnt, information can be stored and displayed in the form of the subject-predicate-object model. To avoid ambiguities and guarantee unambiguity, IRIs are used for the respective parts. We also need a similar approach to these IRIs in the representation and format of the modelling. We need standards in the notation to ensure that the computer handles the data correctly. The standard we want to use in LOD is RDF.

RDF (Resource Description Framework) is a universal data model designed to represent relationships between entities in a structured way. It provides a standardized format for expressing knowledge using the subject-predicate-object model, which allows different datasets to be linked together and ensures interoperability.

Using RDF, we can describe facts in a machine-readable way. Each RDF statement, called a triple, consists of.

For example, we can express the relationship between the painting Wheatfield with Cypresses and Vincent van Gogh using an RDF triple with IRIs:

<https://www.wikidata.org/wiki/Q26221215> <https://www.wikidata.org/wiki/Property:P170> <https://www.wikidata.org/wiki/Q5582>.

This triple means that Wheatfield with Cypresses was painted by Vincent van Gogh.

Using N-Triples as the Simplest RDF Representation

The format used above is called N-Triples, which is the simplest, standardized way to represent RDF data. The basic notation is quite simple. You just need to write your IRIs in angle brackets and end each statement with a period. N-Triples is a line-based format where each fact is written on a single line in the form:

<subject> <predicate> <object>.

This simplicity makes N-Triples easy to parse and store, making it ideal for exchanging RDF data between different systems.

Callout

Writing RDF

  • Write your information in the subject-predicate-object model
  • Use IRIs for the subject, predicate and object
  • Put the IRIs in angle brackets
  • End each statement with a period.

Blank Nodes and Literals in RDF

In RDF, not every object needs a globally unique identifier (IRI). Sometimes, an entity exists that doesn’t need to be explicitly named—this is where Blank Nodes come in.

A Blank Node represents an entity that exists in the data model but has no specific identifier. It is useful when:
- The entity doesn’t have a meaningful global ID.
- It is only relevant in a limited local context.

For example, if a painting has an unknown artist, we might use a blank node to represent the missing information:

<IRI for Unknown Painting> <IRI for "was painted by"> _:b1.

Here, _:b1 is a blank node acting as a placeholder for an unknown artist.

Additionally, RDF supports Literals, which represent concrete values such as dates, numbers, or text instead of links to other entities.

For example, adding the creation year of Wheatfield with Cypresses:

<https://www.wikidata.org/wiki/Q26221215> <"was painted in"> "1889"^^http://www.w3.org/2001/XMLSchema#integer.

This triple states that Wheatfield with Cypresses was painted in the year 1889, with the data type explicitly set as an integer.

Challenge

Exercise: Creating RDF Triples

Convert the following statements or your mindmap from the first task into RDF triples using the correct structure. Use wikidata for IRIs and properties:

  1. Vincent van Gogh was born in Zundert.
  2. Starry Night was painted by Vincent van Gogh.
  3. The painting The Potato Eaters was created in 1885.
<https://www.wikidata.org/wiki/Q5582><https://www.wikidata.org/wiki/Property:P19><https://www.wikidata.org/wiki/Q9883>

<https://www.wikidata.org/wiki/Q45585><https://www.wikidata.org/wiki/Property:P170><https://www.wikidata.org/wiki/Q5582>

<https://www.wikidata.org/wiki/Q154469><https://www.wikidata.org/wiki/Property:P571><"1889"^^http://www.w3.org/2001/XMLSchema#integer>
Key Points

Ressource Description Framework

  • Gives a standardised form to write subject-predicate-object modeled data
  • Is used to connect data on a global scope
  • One Format to write RDF is n-triples
  • Terms are written in angle brackets
  • Statements ending with a period