HTML and CSS Reference
Beyond advanced text editors, there are other programs that cannot be missed from the toolbox of web designers.
Such tools are semantic editors, semantic reasoners, MathML editors, and markup correctors.
Semantic Editors and Reasoners
Along with the increasing popularity of OWL, more and more tools are appearing on the market for OWL
development. Web ontologies are machine-processable, and semantic reasoners (also known as reasoning engines or
rules engines) can be used to infer logical consequences from facts or axioms described by the ontologies. Some of the
most useful semantic editors and reasoners are described next.
Protégé is a free open source framework  and one of the most widely used OWL editors. It is an efficient tool
for developing and testing ontologies. Protégé supports several file formats and syntaxes, including OWL, OWL in
functional syntax, OWL in Manchester syntax, RDF/XML, OBO flat file, KRSS2, Latex, and Turtle. It can directly open
not only saved files but also online ontologies.
HermiT is an OWL Reasoner that can be used to determine ontology consistency, identify relationships between
classes, and perform further tasks. It can be used from the command line, in Java applications, or as a Protégé plug-in
(Figure 11-5 ).
Figure 11-5. The HermiT reasoner running in Protégé