The most important Building Blocks of Linked Data are Ontologies.
OWL and the two Concepts
owl:equivalentClass are rather important to link between Entities that are the same as one links one Entity to another Entity and Classes. Classes are linked with
With OWl one has only the possibility to say that something is the same or something is different.
In-between stating that something is closely the almost the same is difficult. One can not do it with OWL therefore one need another Vocabulary.
One of the large Ontologies or Upper Ontologies use is the UMBEL Ontology, which stands for Upper Mapping and Binding Exchange Layer. It is a Subset of the huge OpenCyc Ontology and is represented as RDF Triples that are based on SKOS and OWL 2. Overall there are more than 20.000 Concepts or Classes represented and more that 46.000 Mappings into DBpedia, geonames, and Datasets with
rdfs:subClassOf. Additionally there are Links to more than 2 million Wikipedia Pages.
To connect Vocabularies and Datasets SKOS is the most important Ontology. SKOS is the Simple Knowledge Organization System which is based on RDF and RDFS. With SKOS one tries to relate two different Ontologies with one another or tow Vocabularies. With SKOS one can define what a Concept is which is similar to and
owl:Class or an
rdf:Class. With the Definitions one can say that something is more general then we use
skos:broader or something is more special then something else, then one uses
skos:narrower. If one wants to say that two things are somehow related then one has the Term
skos:related. Thus it is much more expressive than simply OWL, where one only can say that something is the same or something is different. Then one has also for the equality the possibility to say this is an exact Match, so quite the same as
owl:sameAs even it is more exact as it is really an exact Match. Then there is something like a narrow match (close Match), broad Match and a related Match which are all explained in an informal way by Natural Language. They can be set to related Entities and Classes within Vocabularies with each other. This is rather important.