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I struggle with few definitions in knowledge representation and seek credible help to distinguish between them. I have been searching on wikipedia and many websites for the difference between ontologies and semantic networks (not to be confused with semantic web). While the wikipedia page on semantic network never refer to ontologies, they seem extremely similar and have similar application in CS.

My guess is that semantic network are a type of ontology adapted for research on AI. However, I don't know the difference between both. So my question is simply:

Are semantic networks ontologies? If so, are they synonym? or what are the distinctions?

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    $\begingroup$ there seems to be very strong notions of type theory in ontologies (ideas of instances, classes, attributes), whereas semantic nets don't seem to carry these. Maybe the distinction is akin to the one between untyped lambda calculus and typed lc? $\endgroup$
    – didierc
    Commented Feb 15, 2013 at 23:34

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Semantic Networks are in no way the same as ontologies. The accepted answer is therefore very misleading. Semantic networks (Quillian 1968) and semantic frames (Minsky 1975) emerged earlier than ontologies, and they were lacking a formal semantics despite the fact that they had semantic in the name. This is some kind of a fun fact among logicians: a formalism does not have semantics just because it has it in the name. This has been a basis for a systematic and formal study of ontology languages. Overall, the difference is that ontologies have well-defined, formal semantics whereas semantic networks don't. Let me support this by quoting from "The Description Logic Handbook" (Baader et. al.):

"Owing to their more human-centered origins, the network-based systems were often considered more appealing and more effective from a practical viewpoint than the logical systems. Unfortunately they were not fully satisfactory because of their usual lack of precise semantic characterization."

For more details, please see The Description Logic Handbook, which also contains such historical notes. Currently, ontology languages are much more sophisticated than simple terminologies and encompass a rich logical structure which can not be compared to a network, or so...

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A semantic network is a graphic notation for representing knowledge in patterns of interconnected nodes and arcs. It is one way for knowledge visualization and presentation. It was used firstly for for artificial intelligence and machine translation in computer science. What is common to all semantic networks is a declarative graphic representation that can be used either to represent knowledge or to support automated systems for reasoning about knowledge.

Ontology is a representation vocabulary, specialized to some domain or subject. It is a representation of a set of concepts within a domain and the relationships between those concepts. It is used to reason about the properties of that domain, and may be used to define the domain.

You can find more in references as (specially 4):

1) Sowa, John F., ed. “Principles of Semantic Networks: Explorations in the Representation of Knowledge”, Morgan Kaufmann Publishers, San Mateo, CA, 1991.

2) Noy N.F., McGuinnes D. L. “Ontology Development 101: A Guide to Creating Your First Ontology”. Stanford Knowledge Systems Laboratory Technical Report KSL−01−05 and Stanford Medical Informatics Technical Report SMI−2001−0880, March 2001.

3)María Auxilio, “An Overview of Ontologies”, Center for Research in Information and Automation Technologies Technical Report, Interactive and Cooperative Technologies Lab, Universidad De Las Américas Puebla, México, March 2003.

4) ABDEL-BADEEH M. SALEM, MARCO ALFONSE "Ontology versus Semantic Networks for Medical Knowledge Representation", ICCOMP'08 Proceedings of the 12th WSEAS international conference on Computers, 2008.

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  • $\begingroup$ Still, it does not completely answer the question. I understand that a semantic network could be use to represent an ontology graphically. No wonder ontology is such a controversial word. $\endgroup$
    – Zonata
    Commented Feb 19, 2013 at 0:30
  • $\begingroup$ @Zonata: They are equivalent in some sense. every semantic network could be presented by Ontology and vice Versa. The main diffidence is one is graphical presentation and the other is verbal presentation. $\endgroup$
    – Reza
    Commented Feb 19, 2013 at 0:48

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