Semantic network

# Semantic network

Discussion

Encyclopedia

A semantic network is a network which represents semantic relations among concept
Concept
The word concept is used in ordinary language as well as in almost all academic disciplines. Particularly in philosophy, psychology and cognitive sciences the term is much used and much discussed. WordNet defines concept: "conception, construct ". However, the meaning of the term concept is much...

s. This is often used as a form of knowledge representation
Knowledge representation
Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...

. It is a directed
Directed graph
A directed graph or digraph is a pair G= of:* a set V, whose elements are called vertices or nodes,...

or undirected graph consisting of vertices
Vertex (graph theory)
In graph theory, a vertex or node is the fundamental unit out of which graphs are formed: an undirected graph consists of a set of vertices and a set of edges , while a directed graph consists of a set of vertices and a set of arcs...

, which represent concept
Concept
The word concept is used in ordinary language as well as in almost all academic disciplines. Particularly in philosophy, psychology and cognitive sciences the term is much used and much discussed. WordNet defines concept: "conception, construct ". However, the meaning of the term concept is much...

s, and edges
Graph theory
In mathematics and computer science, graph theory is the study of graphs, mathematical structures used to model pairwise relations between objects from a certain collection. A "graph" in this context refers to a collection of vertices or 'nodes' and a collection of edges that connect pairs of...

.

## History

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.

"Semantic Nets" were first invented for computers by Richard H. Richens
Richard H. Richens
Richard H. Richens was the inventor of semantic nets for computers. While at the Cambridge Language Research Unit, in 1956 he created semantic nets as an "interlingua" for machine translation of natural languages...

of the Cambridge Language Research Unit in 1956 as an "interlingua
Pivot language
A pivot language, sometimes also called a bridge language, is an artificial or natural language used as an intermediary language for translation between many different languages – to translate between any pair of languages A and B, one translates A to the pivot language P, then from P to B...

" for machine translation
Machine translation
Machine translation, sometimes referred to by the abbreviation MT is a sub-field of computational linguistics that investigates the use of computer software to translate text or speech from one natural language to another.On a basic...

of natural language
Natural language
In the philosophy of language, a natural language is any language which arises in an unpremeditated fashion as the result of the innate facility for language possessed by the human intellect. A natural language is typically used for communication, and may be spoken, signed, or written...

s.

They were developed by Robert F. Simmons at System Development Corporation
System Development Corporation
System Development Corporation , based in Santa Monica, California, was considered the world's first computer software company.SDC started in 1955 as the systems engineering group for the SAGE air defense ground system at the RAND Corporation...

in the early 1960s and later featured prominently in the work of Allan M. Collins
Allan M. Collins
Allan M. Collins is an American cognitive scientist and Professor Emeritus of Learning Sciences at Northwestern University's School of Education and Social Policy...

and colleagues (e.g., Collins and Quillian; Collins and Loftus).

In the 1960s to 1980s the idea of a semantic link was developed within hypertext
Hypertext
Hypertext is text displayed on a computer or other electronic device with references to other text that the reader can immediately access, usually by a mouse click or keypress sequence. Apart from running text, hypertext may contain tables, images and other presentational devices. Hypertext is the...

systems as the most basic unit, or edge, in a semantic network. These ideas were extremely influential, and there have been many attempts to add typed link
A typed link in a hypertext system is a link to another document or part of a document that includes information about the character of the link...

semantics to HTML
HTML
HyperText Markup Language is the predominant markup language for web pages. HTML elements are the basic building-blocks of webpages....

and XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....

.

### Definition

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

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
Spreading activation is a method for searching associative networks, neural networks, or semantic networks. The search process is initiated by labeling a set of source nodes with weights or "activation" and then iteratively propagating or "spreading" that activation out to other nodes linked to...

, inheritance
Inheritance
Inheritance is the practice of passing on property, titles, debts, rights and obligations upon the death of an individual. It has long played an important role in human societies...

, 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

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.

### Semantic Net in Lisp

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'd use the "assoc" function with a key of "canary" to extract all the information about the "canary" type.

### WordNet

An example of a semantic network is WordNet
WordNet
WordNet is a lexical database for the English language. It groups English words into sets of synonyms called synsets, provides short, general definitions, and records the various semantic relations between these synonym sets...

, a lexical
Lexicon
In linguistics, the lexicon of a language is its vocabulary, including its words and expressions. A lexicon is also a synonym of the word thesaurus. More formally, it is a language's inventory of lexemes. Coined in English 1603, the word "lexicon" derives from the Greek "λεξικόν" , neut...

database of English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...

. 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
Meronymy
Meronymy is a semantic relation used in linguistics. A meronym denotes a constituent part of, or a member of something. That is,...

(A is part of B, i.e. B has A as a part of itself), holonymy
Holonymy
Holonymy is a semantic relation. Holonymy defines the relationship between a term denoting the whole and a term denoting a part of, or a member of, the whole. That is,...

(B is part of A, i.e. A has B as a part of itself), hyponymy (or troponymy
Troponymy
Troponymy is the presence of a ‘manner’ relation between two lexemes.The notion was originally proposed by Christiane Fellbaum and George Miller. Some examples they gave are “to nibble is to eat in a certain manner, and to gorge is to eat in a different manner...

) (A is subordinate of B; A is kind of B), hypernym
Hypernym
In linguistics, a hyponym is a word or phrase whose semantic field is included within that of another word, its hypernym . In simpler terms, a hyponym shares a type-of relationship with its hypernym...

y (A is superordinate of B), synonym
Synonym
Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

y (A denotes the same as B) and antonym
Antonym
In lexical semantics, opposites are words that lie in an inherently incompatible binary relationship as in the opposite pairs male : female, long : short, up : down, and precede : follow. The notion of incompatibility here refers to the fact that one word in an opposite pair entails that it is not...

y (A denotes the opposite of B).

WordNet properties have been studied from a network theory
Graph theory
In mathematics and computer science, graph theory is the study of graphs, mathematical structures used to model pairwise relations between objects from a certain collection. A "graph" in this context refers to a collection of vertices or 'nodes' and a collection of edges that connect pairs of...

perspective and compared to other semantic networks created from Roget's Thesaurus
Roget's Thesaurus
Roget's Thesaurus is a widely-used English language thesaurus, created by Dr. Peter Mark Roget in 1805 and released to the public on 29 April 1852. The original edition had 15,000 words, and each new edition has been larger...

and word association
Word Association
Word Association is a common word game involving an exchange of words that are associated together. The game is based on the noun phrase word association, meaning "stimulation of an associative pattern by a word" or "the connection and production of other words in response to a given word, done...

tasks. From this perspective the three of them are a small world structure
Small-world network
In mathematics, physics and sociology, a small-world network is a type of mathematical graph in which most nodes are not neighbors of one another, but most nodes can be reached from every other by a small number of hops or steps...

.

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
John F. Sowa
John Florian Sowa is the computer scientist who invented conceptual graphs, a graphic notation for logic and natural language, based on the structures in semantic networks and on the existential graphs of Charles S. Peirce. He is currently developing high-level "ontologies" for artificial...

. 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

Other examples of semantic networks are Gellish
Gellish
Gellish is a controlled natural language, also called a formal language, in which information and knowledge can be expressed in such a way that it is computer-interpretable, as well as system-independent. Gellish is a structured subset of natural language that is suitable for information modelling...

models. Gellish English
Gellish English
Gellish English is a variant of Gellish and is a formal language, which means that it is structured and formalised subset of natural English that is computer interpretable. Its definition includes an English dictionary of concepts that is arranged in a taxonomy and that is extended into an ontology...

with its Gellish English dictionary
Gellish English dictionary
The Gellish English Dictionary-Taxonomy is an example of an open-source “smart” electronic dictionary, which concepts are arranged in a subtype-supertype hierarchy, thus forming a taxonomy. The dictionary-taxonomy is a machine readable...

, is a formal language
Formal language
A formal language is a set of words—that is, finite strings of letters, symbols, or tokens that are defined in the language. The set from which these letters are taken is the alphabet over which the language is defined. A formal language is often defined by means of a formal grammar...

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
Gellish database
-Universal data structure:Gellish databases are semantic databases that all have the same universally applicable data structure. That data structure is suitable to contain any fact that is expressed in a Gellish language variant, such as Gellish English or Gellish Dutch...

and is computer interpretable.

## Software tools

There are also elaborate types of semantic networks connected with corresponding sets of software tools used for lexical knowledge engineering
Knowledge engineering
Knowledge engineering was defined in 1983 by Edward Feigenbaum, and Pamela McCorduck as follows:At present, it refers to the building, maintaining and development of knowledge-based systems...

, like the Semantic Network Processing System (SNePS
SNePS
SNePS is a knowledge representation, reasoning, and acting system developed and maintained by Stuart C. Shapiro and colleagues at the State University of New York at Buffalo....

) of Stuart C. Shapiro or the MultiNet
MultiNet
Multilayered extended semantic networks are both a knowledge representation paradigm and a language for meaning representation of natural language expressions that has been developed by Prof. Dr. Hermann Helbig on the basis of earlier Semantic Networks.MultiNet is claimed to be one of the most...

paradigm of Hermann Helbig, especially suited for the semantic representation of natural language expressions and used in several NLP
Natural language processing
Natural language processing is a field of computer science and linguistics concerned with the interactions between computers and human languages; it began as a branch of artificial intelligence....

applications.

• Conceptual graph
Conceptual graph
Conceptual graphs are a formalism for knowledge representation. In the first published paper on CGs, John F. Sowa used them to represent the conceptual schemas used in database systems...

• Knowledge representation
Knowledge representation
Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...

• Mind map
Mind map
A mind map is a diagram used to represent words, ideas, tasks, or other items linked to and arranged around a central key word or idea. Especially in British English, the terms spidergram and spidergraph are more common, but they can cause confusion with the term spider diagram used in mathematics...

• Network diagram
Network diagram
A computer network diagram is a schematic depicting the nodes and connections amongst nodes in a computer network or, more generally, any telecommunications network.-Symbolization:...

• Semantic lexicon
Semantic lexicon
A semantic lexicon is a dictionary of words labeled with semantic classes so associations can be drawn between words that have not previously been encountered: it is a dictionary with a semantic network.-List of semantic lexicons:*WordNet*EuroWordNet...

• Semantic Web
Semantic Web
The Semantic Web is a collaborative movement led by the World Wide Web Consortium that promotes common formats for data on the World Wide Web. By encouraging the inclusion of semantic content in web pages, the Semantic Web aims at converting the current web of unstructured documents into a "web of...

• Semantic computing
Semantic computing
Semantic computing is a field of computing that combines elements of semantic analysis, natural language processing, data mining and related fields.Semantic computing addresses three core problems:...

• Semantic neural network
Semantic neural network
Semantic neural network is based on John von Neumann's neural network [von Neumann, 1966] and Nikolai Amosov M-Network. There are limitations to a link topology for the von Neumann’s network but SNN accept a case without these limitations. Only logical values can be processed, but SNN accept that...

• Unified Medical Language System
Unified Medical Language System
The Unified Medical Language System is a compendium of many controlled vocabularies in the biomedical sciences . It provides a mapping structure among these vocabularies and thus allows one to translate among the various terminology systems; it may also be viewed as a comprehensive thesaurus and...

(UMLS)
• Word sense disambiguation
Word sense disambiguation
In computational linguistics, word-sense disambiguation is an open problem of natural language processing, which governs the process of identifying which sense of a word is used in a sentence, when the word has multiple meanings...

(WSD)