Semantic network

A semantic network, or frame network, is a network which represents semantic relations between concepts. This is often used as a form of knowledge representation. It is a directed or undirected graph consisting of vertices, which represent concepts, and edges.^[1]

History [edit]

Example of a semantic network

In 1909, Charles S. Peirce proposed a graphical notation of nodes and edges called "existential graphs" that he called "the logic of the future". This began the debate between advocates of "logic" and advocates of "semantic networks." This debate obscured the fact that semantics networks, at least those with well-defined semantics, are a form of logic.^[2]

"Semantic Nets" were first invented for computers by Richard H. Richens of the Cambridge Language Research Unit in 1956 as an "interlingua" for machine translation of natural languages.

They were developed by Robert F. Simmons ^[3] and M. Ross Quillian ^[4] at System Development Corporation in the early 1960s. It later featured prominently in the work of Allan M. Collins and Quillian (e.g., Collins and Quillian;^[5][6] Collins and Loftus^[7] Quillian ^{[8][9][10][11]})

Basics of semantic networks [edit]

Definition [edit]

A semantic network is used when one has knowledge that is best understood as a set of concepts that are related to one another.

More generally [edit]

Most semantic networks are cognitively based. They also consist of arcs and nodes which can be organized into a taxonomic hierarchy. Semantic networks contributed ideas of spreading activation, inheritance, and nodes as proto-objects. They are intractable for large domains. Finally they don't represent performance or meta-knowledge very well.

Things to remember about semantic networks [edit]

Some properties are not easily expressed using a semantic network, e.g., negation, disjunction, and general non-taxonomic knowledge. Expressing these relationships requires workarounds, such as having complementary predicates and using specialized procedures to check for them, but this can be regarded as less elegant.^{[citation needed]}

Examples [edit]

Semantic Net in Lisp [edit]

Using an association list.

(defun *database* ()
'((canary  (is-a bird)
               (color yellow)
               (size small))
   (penguin (is-a bird)
                  (movement swim))
   (bird    (is-a vertebrate)
               (has-part wings)
               (reproduction egg-laying))))

You would use the "assoc" function with a key of "canary" to extract all the information about the "canary" type.^[12]

WordNet [edit]

An example of a semantic network is WordNet, a lexical database of English. It groups English words into sets of synonyms called synsets, provides short, general definitions, and records the various semantic relations between these synonym sets. Some of the most common semantic relations defined are meronymy (A is part of B, i.e. B has A as a part of itself), holonymy (B is part of A, i.e. A has B as a part of itself), hyponymy (or troponymy) (A is subordinate of B; A is kind of B), hypernymy (A is superordinate of B), synonymy (A denotes the same as B) and antonymy (A denotes the opposite of B).

WordNet properties have been studied from a network theory perspective and compared to other semantic networks created from Roget's Thesaurus and word association tasks. From this perspective the three of them are a small world structure.^[13]

Other examples [edit]

It is also possible to represent logical descriptions using semantic networks such as the existential Graphs of Charles Sanders Peirce or the related Conceptual Graphs of John F. Sowa.^[1] These have expressive power equal to or exceeding standard first-order predicate logic. Unlike WordNet or other lexical or browsing networks, semantic networks using these representations can be used for reliable automated logical deduction. Some automated reasoners exploit the graph-theoretic features of the networks during processing.

Other examples of semantic networks are Gellish models. Gellish English with its Gellish English dictionary, is a formal language that is defined as a network of relations between concepts and names of concepts. Gellish English is a formal subset of natural English, just as Gellish Dutch is a formal subset of Dutch, whereas multiple languages share the same concepts. Other Gellish networks consist of knowledge models and information models that are expressed in the Gellish language. A Gellish network is a network of (binary) relations between things. Each relation in the network is an expression of a fact that is classified by a relation type. Each relation type itself is a concept that is defined in the Gellish language dictionary. Each related thing is either a concept or an individual thing that is classified by a concept. The definitions of concepts are created in the form of definition models (definition networks) that together form a Gellish Dictionary. A Gellish network can be documented in a Gellish database and is computer interpretable.

Software tools [edit]

There are also elaborate types of semantic networks connected with corresponding sets of software tools used for lexical knowledge engineering, like the Semantic Network Processing System (SNePS) of Stuart C. Shapiro^[14] or the MultiNet paradigm of Hermann Helbig,^[15] especially suited for the semantic representation of natural language expressions and used in several NLP applications.

Semantic networks are used in specialized information retrieval tasks, such as plagiarism detection. They provide information on hierarchical relations in order to employ semantic compression to reduce language diversity and enable the system to match word meanings, independently from sets of words used.

See also [edit]

• Abstract semantic graph
• Conceptual graph
• Knowledge representation
• Mind map
• Network diagram
• Semantic lexicon
• Semantic Web
• Semantic computing
• Semantic neural network
• Taxonomy (general)
• Unified Medical Language System (UMLS)
• Word sense disambiguation (WSD)

Examples [edit]

• Lexipedia
• WordNet
• SNOMED CT
• ConceptNet

References [edit]

Further reading [edit]

• Allen, J. and A. Frisch (1982). "What's in a Semantic Network". In: Proceedings of the 20th. annual meeting of ACL, Toronto, pp. 19-27.
• John F. Sowa, Alexander Borgida (1991). Principles of Semantic Networks: Explorations in the Representation of Knowledge.

External links [edit]

Wikimedia Commons has media related to: Semantic networks

• "Semantic Networks" by John F. Sowa
• "Semantic Link Network" by Hai Zhuge