What is an N-Triple?
An N-Triple is a fundamental, line-based plain text format used to encode information within an RDF graph, representing a single piece of a statement in the Resource Description Framework (RDF). It is a simple, human-readable serialization format designed for easy parsing and generation.
Understanding the Core Structure
At its heart, an N-Triple follows a straightforward subject-predicate-object pattern, much like a grammatical sentence. Each component plays a distinct role:
- Subject: The entity or resource being described. This can be an Internationalized Resource Identifier (IRI) (a unique web address-like identifier) or a blank node (an unnamed resource).
- Predicate: The property or characteristic of the subject, expressed as an IRI, describing the relationship between the subject and the object.
- Object: The value of the property, which can be an IRI, a blank node, or a literal (a data value like a string, number, or date).
The Evolution with Triple Terms
While the basic subject-predicate-object structure is standard for RDF, the RDF 1.2 N-Triples specification introduced a significant enhancement: triple terms.
Traditionally, subjects and objects in RDF triples were limited to IRIs, blank nodes, or literals. With the introduction of triple terms:
- A complete RDF triple itself can now act as the subject or object of another triple. This means an entire statement can become a component of a larger statement.
- This powerful feature enables the ability to make statements about other statements. For instance, one could assert who made a specific statement, when it was made, or express a degree of certainty about it.
How Triple Terms Expand Expressiveness
This addition is crucial for scenarios requiring more nuanced data representation in Knowledge Graphs and the Semantic Web, such as:
- Provenance: Recording who asserted a statement or the time it was valid.
- Context: Specifying the conditions or source under which a statement is true.
- Beliefs/Assertions: Attributing statements to specific entities or expressing levels of certainty and contradiction.
N-Triple Syntax and Examples
The syntax of an N-Triple is straightforward: each triple is written on a single line and ends with a period (.).
Consider these examples demonstrating the format:
| Type | Example | Explanation |
|---|---|---|
| Basic Triple | <http://example.org/person/alice> <http://xmlns.com/foaf/0.1/name> "Alice" . |
Alice (subject) has a name (predicate) "Alice" (object). |
| Blank Node | _:b1 <http://xmlns.com/foaf/0.1/age> "30"^^<http://www.w3.org/2001/XMLSchema#integer> . |
An unnamed person (blank node _:b1) has an age (predicate) of 30 (typed literal representing an integer). |
| Triple Term | <http://example.org/report/123> <http://example.org/property/reports> <<http://example.org/city/london> <http://example.org/property/hasPopulation> "9000000">> . |
Report 123 (subject) reports (predicate) on the statement that "London has a population of 9,000,000" (the entire inner triple acts as the object, making a statement about another statement). |
Applications and Significance
N-Triples are widely used in contexts related to the Semantic Web and Knowledge Graphs due to their simplicity and clarity. They provide a foundational mechanism for expressing relationships and data in a machine-readable yet human-interpretable way, fostering data interoperability across disparate systems. Their line-based nature makes them easy to parse and generate, making them a common choice for sharing and processing large volumes of RDF data efficiently.
