The Web Ontology Language (OWL [2]) is the W3C’s standard
for representing Semantic Web ontologies and has been
adopted by most biomedical ontology development efforts.
OWL ontologies can be used along with RDF data because
OWL uses the RDF syntax. RDF’s abstract triple syntax has
a graph nature. The RDF graph is defined as a set of triples
and can be viewed as a directed labeled graph (DG). One
disadvantage of DG is that it makes an artificial distinction
between resources and properties, which leads to incongruous
representations (e.g., properties are usually represented as arcs,
but in meta-statement about the properties themselves, the
properties have to be represented as nodes).