# Metadata as Relations Between Identifiers

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

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 ↩︎