Reuse of standard vocabularies

The underlying idea of adopting existing vocabularies is to enable an optimal reuse of the work that has already been done and acknowledged on linked data. In this way, it is not only possible to create datasets based on proved solutions easier and faster than starting from scratch, but also contribute to a proper expansion of the Web of data, by clearly linking new datasets to existing and commonly adopted resources. 
When reusing existing vocabularies, it is important to first take the time to look for what is currently available. For example, there are several vocabularies for linked data suggested by the W3C. An overview of vocabularies is provided in the following table.
Name 	Prefix	Namespace URI 	Describes
WGS84 	geo: 	http://www.w3.org/2003/01/geo/ 	geo positioning
Bibliographic Ontology 	bibo: 	http://purl.org/ontology/bibo/ 	Bibliographies
Creative Commons Rights Expression Language	cc: 	http://creativecommons.org/ns 	Licenses
Data Catalog Vocabulary 	dcat: 	http://www.w3.org/TR/vocab-dcat/ 	Datasets
Data Cube Vocabulary 	qb: 	http://www.w3.org/TR/vocab-data-cube/ 	Multi-dimensional data
Description of a Project 	doap: 	http://usefulinc.com/ns/?doap 	Projects
Dublin Core Metadata Initiative 	dct: 	http://dublincore.org/documents/dcmi-terms/ 	Publications
Friend-of-a-Friend 	foaf: 	http://xmlns.com/foaf/spec/ 	People
GeoNames Ontology 	gn: 	http://www.geonames.org/ontology/ontology_v2.2.1.rdf	Locations
Good Relations 	gr: 	http://purl.org/goodrelations/v1 	Products
Object Reuse and Exchange 	ore: 	http://www.openarchives.org/ore/ 	Resource maps
Organization Ontology 	org: 	http://www.w3.org/TR/vocab-org/ 	Organizations
Semantically-Interlinked Online Communities	sioc: 	http://rdfs.org/sioc/spec/ 	Online Communitites
vCard 	vcard:	http://w3.org/TR/vcard-rdf/ 	Business cards
Vocabulary of Interlinked Datasets 	void: 	http://www.w3.org/2001/sw/interest/void/ 	Vocabularies
In addition, it is possible to find existing vocabularies using dedicated search engines for the Semantic Web (e.g., Watson, Sindice, Semantic Web Search Engine, Swoogle, and Schemapedia), and other platforms, such as the LOV directory, Prefix.cc, Bioportal for the biological domain, and the European Commission's Joinup platform. 
Once a potential vocabulary has been identified, one should critically review this vocabulary according to the following criteria in order to decide whether to adopt it or not:
*The vocabulary must be well documented by using label and comment annotations. Moreover, a human-readable page should be available to describe classes and properties, possibly including use cases that show the vocabulary’s applicability. 
*The vocabulary should be self-descriptive by using at least a label, a definition and a comment for each class or property.
*The vocabulary should be described in several languages, especially when publishing government data, by using labels, definitions and comments in the government's official language(s) and at least in English.
*The vocabulary should be used by other datasets to guarantee acknowledgement in the LOD community and promote reuse of high quality contributions.
*The vocabulary should be accessible for a long period by providing some guarantee of maintenance over a specified period, ideally indefinitely.
*The vocabulary should be published by a trusted group or organization since anyone can in principle create a vocabulary, it is always better to check whether there is a person, group or authoritative organization that is responsible for publishing and maintaining the vocabulary.
*The vocabulary should have a persistent URL to guarantee persistent access to the server hosting the vocabulary.
*The vocabulary should provide a versioning policy to guarantee that the publisher will address compatibility of versions over time. Major changes to the vocabularies should be reflected in the documentation. 
Another good source before starting with defining new vocabularies is the http://sameas.org website, which contains a collection of triples that contain the “owl:sameas” construct. The “owl:sameas” construct is also useful when you find out that a term in someone else’s vocabulary means the same thing in your own vocabulary. In that situation it is not necessary to change your vocabulary but to only publish a triple with owl:sameas. Note: owl:sameas should only be used for relating two pure synonyms, i.e., two terms that refer to exactly the same concept. If the relationship is less precise, owl:subClassOf may be used to relate one concept to a slightly more general concept.
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