Editing Symbolic artificial intelligence (section)

==== Knowledge representation ====
{{Main|Knowledge Representation}}

[[Semantic networks]], [[conceptual graphs]], [[Frame (artificial intelligence)|frames]], and [[formal logic|logic]] are all approaches to modeling knowledge such as domain knowledge, problem-solving knowledge, and the semantic meaning of language. [[Ontologies]] model key concepts and their relationships in a domain. Example ontologies are [[YAGO (database)|YAGO]], [[WordNet]], and [[Upper ontology#DOLCE|DOLCE]]. [[Upper ontology#DOLCE|DOLCE]] is an example of an [[upper ontology]] that can be used for any domain while WordNet is a lexical resource that can also be viewed as an [[upper ontology#WordNet|ontology]]. YAGO incorporates WordNet as part of its ontology, to align facts extracted from [[Wikipedia]] with WordNet [[synsets]]. The [[Disease Ontology]] is an example of a medical ontology currently being used.

[[Description logic]] is a logic for automated classification of ontologies and for detecting inconsistent classification data. [[Web Ontology Language|OWL]] is a language used to represent ontologies with [[description logic]]. [[Protégé (software)|Protégé]] is an ontology editor that can read in [[Web Ontology Language|OWL]] ontologies and then check consistency with [[deductive classifier]]s such as such as HermiT.<ref name="HermiT">{{Cite journal| doi = 10.1613/jair.2811| issn = 1076-9757| volume = 36| pages = 165–228| last1 = Motik| first1 = Boris| last2 = Shearer| first2 = Rob| last3 = Horrocks| first3 = Ian| title = Hypertableau Reasoning for Description Logics| journal = Journal of Artificial Intelligence Research| date = 2009-10-28| arxiv = 1401.3485| s2cid = 190609}}</ref>

First-order logic is more general than description logic. The automated theorem provers discussed below can prove theorems in first-order logic. [[Horn clause]] logic is more restricted than first-order logic and is used in logic programming languages such as Prolog. Extensions to first-order logic include [[temporal logic]], to handle time; [[epistemic logic]], to reason about agent knowledge; [[modal logic]], to handle possibility and necessity; and [[probabilistic logic]]s to handle logic and probability together.