Metadata as Relations Between Identifiers

An item of metadata is a relationship that someone claims to exist between two entities.1

With linked data, then,

all metadata can be expressed in terms of relationships between identifiers.2

Consider that in RDF, even literals are objects. A triple with a “literal value” V as its object is a relationship with an implicit identifier associated with the value V and also associated with a type and a language:

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
<#it> rdfs:label "book" .
<#it> rdfs:label "book"^^xsd:string . # type explicit
<#it> rdfs:label "book"^^xsd:string@en . # language explicit

This may be more clear in a JSON-LD representation, where a literal may be represented as a JSON object with a @value field and with optional fields @type (which defaults to xsd:string) and @language (which defaults to en), i.e.

"book"
{"@value": "book"}
{"@value": "book", "@type": "xsd:string"}
{"@value":  "book", "@type": "xsd:string", "@language": "en"}

are equivalent. It seems helpful to explicitly associate an identifier with all literal values in an information system, i.e. an @id field for a JSON-LD representation, even if the @id URL is not externally resolvable and the entity’s value is inlined as @value rather than fetched separately.


  1. G. Rust and M. Bide, “The metadata framework: Principles, model and data dictionary,” Jun. 2000. [Online]. Available: https://www.doi.org/topics/indecs/indecs_framework_2000.pdf ↩︎

  2. M. Bide, “Standard Identifiers: an overview of the current landscape,” presented at the USPTO Open Meeting: Facilitating the Development of the Online Licensing Environment for Copyrighted Works, Apr. 01, 2015. [Online]. Available: pdf ↩︎