Vocabularies in iSamples are used to provide discrete labels that help to categorize samples. The vocabularies are generally hierarchical in nature with a top level broad concept and progressively narrower concepts. Relationship between the concepts are defined using the Simple Knowledge Organization System (SKOS) common data model.

Vocabulary Components

Herein skos refers to http://www.w3.org/2004/02/skos/core#

A vocabulary as used in iSamples is an RDF graph composed of one instance of skos:ConceptScheme and one or more instances of skos:Concept.

One or more of the skos:Concept instances should include a skos:topConceptOf predicate, the object of which is the skos:ConceptScheme for the vocabulary. If a skos:Concept does not include a skos:topConceptOf predicate, then it should contain a skos:inScheme predicate that refers to the skos:ConceptScheme instance.^[1]

A skos:Concept instance that does not include a skos:topConceptOf predicate must include a skos:broader predicate, the object of which is an instance of skos:Concept with a broader definition.

Each skos:Concept instance must include a skos:prefLabel and should include a skos:definition that provides a clear textual description of the concept.^[2]

@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix eg: <https://example.net/my/minimal/> .

eg:vocab
    rdf:type skos:ConceptScheme ;
    skos:prefLabel "Minimal Example Vocabulary"@en ;
.

eg:thing
    rdf:type skos:Concept ;
    skos:topConceptOf eg:vocab ;
    skos:prefLabel "thing"@en ;
    skos:definition "Any physical thing"@en ;
.

eg:solid
    rdf:type skos:Concept ;
    skos:inScheme eg:vocab ;
    skos:broader eg:thing ;
    skos:prefLabel "solid"@en ;
    skos:definition "A thing that was considered solid at the time of observation"@en ;
.

Example. A minimal vocabulary that defines two concepts "thing" and "living_thing" within the vocabulary <https://example.net/my/minimal/vocabulary>.

Extending a Vocabulary

A vocabulary extension is used to augment an existing vocabulary, typically by adding more narrowly construed concepts ("narrower terms").

In iSamples, a vocabulary extension is a vocabulary where the skos:ConceptScheme instance includes a skos:inScheme predicate that refers to the skos:ConceptScheme of the vocabulary being extended. This is used programmatically to identify the vocabulary being extended and to help ensure that skos:Concept instances directly or indirectly extend the base vocabulary.

An extension vocabulary must include one or more instances of skos:Concept. Each instance must have a skos:broader predicate. Following a path of skos:broader properties must lead to a skos:Concept that is a skos:topConceptOf the base vocabulary directly or indirectly referred to by the skos:inScheme property of the skos:ConceptScheme instance of the extension vocabulary.

@prefix owl: <http://www.w3.org/2002/07/owl#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix skos: <http://www.w3.org/2004/02/skos/core#> .
@prefix eg: <https://example.net/my/minimal/> .
@prefix ext: <https://example.net/my/extension/> .

ext:vocab
    rdf:type skos:ConceptScheme ;
    skos:prefLabel "Simple Vocabulary Extension"@en ;
    skos:inScheme eg:vocab ;
.    

ext:liquid 
    rdf:type skos:Concept ;
    skos:prefLabel "liquid"@en ;
    skos:definition "A thing that was considered to be of a liquid state at the time of observation"@en ;
    skos:inScheme ext:vocab ;
    skos:broader eg:thing ;
.

Example. An extension vocabulary that extends <https://example.net/my/minimal/vocabulary> with a single concept.

Other Semantic Relations

In many cases it is desireable to cross reference vocabulary concepts with concepts defined elsewhere. There are several skos predicates describing semantic and mapping relations that can be helpful for describing the relationships between terms and vocabularies. These include:

• skos:narrower
• skos:related
• skos:broaderTransitive
• skos:narrowerTransitive
• skos:closeMatch
• skos:exactMatch
• skos:broadMatch
• skos:narrowMatch
• skos:relatedMatch

---

1. The containing vocabulary may be inferred by traversing semantic relations such as skos:broader to find a semantically related concept that includes skos:inScheme or skos:topConceptOf, but including skos:inScheme with each concept provides a more explicit construct for consumers. ↩︎

2. Only one skos:prefLabel and one skos:definition per language is permitted. ↩︎