Alignment with SKOS
A key tenet of the RDF vision is to link the vast amounts of unstructured (i.e., human-readable) information available by providing structure and semantic meaning, leading to beneficial outcomes for understanding, discovering, and sharing that information. The xAPI Vocabulary Dataset Schema is aligned with RDF and SKOS to achieve the same beneficial outcomes. SKOS, is a model for sharing or linking the meaning of related concepts. It also provides options for labels and definition translations in any language. It is commonly used for designing knowledge representations such as thesauri, classification schemes, taxonomies, subject-heading systems, or any other type of structured, controlled vocabulary. The design of the xAPI Vocabulary Dataset Schema is primarily aligned with SKOS because it provides specific guidelines and options for expressing relationships between concepts (vocabulary terms) and associating them within concept schemes (vocabularies).
xAPI Verbs and Activity Types as Concepts
In SKOS, a concept is intended to represent items in a particular knowledge domain. In the section Semantic Web Technology, Linked Data, and RDF of this document, non-information resources are defined as things that can’t be transmitted electronically. One of these types of possible non-information resources is a “concept.” Verbs and Activity Types fall into this category of abstract concepts. A concept can have multiple labels, but only one of these for each language can be related as a preferred label. Concepts can also be documented using different types of notes, such as definitions, scope notes, editorial notes, or history notes. SKOS further allows the establishment of links between concepts known as semantic relationships. Fully annotating these relationships in RDF is optional at this time, but will become more widely supported once the xAPI community has implemented a curation process or a tool to support it. Concepts are intended to be linked to and associated with concept schemes (i.e., vocabularies).
xAPI Vocabularies as Concept Schemes
Instances of the skos:ConceptScheme class are intended to aggregate instances of the skos:Concept class. In other words, a SKOS concept scheme is the aggregation of one or more SKOS concepts, for the purpose of this specification, a concept scheme is analogous to an xAPI vocabulary. Therefore, the skos:ConceptScheme class is used exclusively in the xAPI Vocabulary Dataset Schema to represent any type of xAPI vocabulary list of Verbs and/or Activity Types. SKOS does not constrain a concept to be contained within only one particular scheme. In other words, concepts (Verbs and Activity Types) can be associated with multiple concept schemes (vocabularies). This association is handled using the skos:inScheme property. Refer to Appendix A for an example in HTML of how each of the cmi5 verbs (concept) IRIs are connected to the vocabulary (concept scheme) IRI, https://w3id.org/xapi/cmi5. Refer to the xAPI Vocabulary Primer for more examples.