Universal Words

Universal Words, or simply UWs, are the words of UNL, and correspond to the nodes - to be interlinked by relations and specified by attributes - in a UNL graph. The set of UWs is open, and constitutes the lexicon of UNL.

Definition

The basic assumption of the UNL approach is that the information conveyed by natural languages can be formally represented through three different types of discrete semantic units: UWs, attributes and relations. This three-layered representation model is the cornerstone of UNL and its most distinctive feature over other semantic networks, which normally proposes only two levels: edges and vertices. Nevertheless, it poses several problems to the UNLization as the distinction between what is supposed to be represented by each unit is not always clear.

The main difficulty concerns what is to be represented as a UW (i.e., as a node in the UNL graph) and what is to be represented as a relation between UWs. How many UWs are there, for instance, in the sentence "Charles Dickens was the author of Oliver Twist"? Should "author" be represented as a UW or as a relation between "Charles Dickens" and "Oliver Twist"? Should the verb "to be" be represented as a UW or as a relation between "Charles Dickens" and "author"? Should the preposition "of" be represented as a UW or as a relation between "author" and "Oliver Twist"?

Given the difficulty to clearly define the concept of "concept", the UNL assumes that UWs must correspond to and only to semantic discrete units that correspond to natural language open lexical categories (noun, verb, adjective and adverb). Any other semantic content (such as the ones conveyed by articles, prepositions, conjunctions etc.) should be represented as attributes or relations. This criterion is not language-biased: if a given semantic value proves to be conveyed, in any language, by a closed class, it should not be represented as a UW, regardless of its realisation in other languages.

Types of UWs

Permanent UWs and Temporary UWs

UWs can be permanent or temporary.

Permanent UWs

Permanent UWs are included in the UNL Dictionary and correspond to well-established lexemes. They can be simple, compound or complex (see below).

Temporary UWs

Temporary UWs are words that:

• Represent concepts or entities that are still candidates to be included in the UNL Dictionary ("Barack Obama", "Twitter");
• Are too specific to be included in the UNL Dictionary ("Universal Networking Digital Language Foundation", "Léon Werth"); or
• Are not translatable ("3.14159", "H₂O", "www.undlfoundation.org");

Temporary UWs are always represented between "double quotes", and observe the source language spelling practices (concerning, for instance, capitalization). For the time being, they are also expected to be transliterated in Roman characters.

Simple UWs, Compound UWs and Complex UWs

Permanent UWs can be simple, compound or complex.

Simple UWs

A simple UW is an isolated node in the UNL graph. It has been represented either as an integer or as a a unique character-string split into two different parts: a root and a suffix. The root can be a word or a multiword expression; the suffix, which is always introduced by a UNL relation, is used to disambiguate the root, i.e., to assign uniqueness to the UW.

Example of a simple UW

UNL Representation		NL Representation
104379964		table(icl>furniture) table(icl>mobilier) mesa(icl>mobiliario) Tisch(icl>Möbel) стол(icl>мебель) ...

Compound UWs

A compound UW is an isolated node combined with attributes. It is used when the concept can be fully derived from the combination of an existing simple UW and a UNL attribute, such as the concept conveyed by the English word "bigger", which can be represented simply as the UW corresponding to "big" ("301382086" or "big(aoj>thing)") specified by the degree attribute "@more": 301382086.@more or big(aoj>thing).@more.

Complex UWs

A complex UW is a hyper-node, i.e., a sub-graph inside the UNL graph. As graphs, complex UWs follow the structure defined for UNL Sentences. They are used when the concept can be fully derived from the combination of existing UWs, relations and attributes, such as in the case of the English multiword expression "pay attention", which could be represented, for instance, as obj(200732224,105702275) or obj(pay(agt>person,obj>thing),attention(icl>faculty).

Principles

Sense

UWs represent sense and not reference. UWs are related to the intension (sense, meaning, connotation) rather than to the extension (reference, denotation) of linguistic expressions. The expressions "morning star" and "evening star", which are said to have the same reference (the planet Venus), must be necessarily represented by different UWs, because they convey different ""modes of presentation" of the same object, i.e., have different senses: "the last star to disappear in the morning" and "the first star to appear in the evening", respectively.

Productivity

UWs must correspond to and only to contents lexicalized by natural language open lexical categories (nouns, verbs, adjectives and adverbs). Any other semantic content (such as the ones conveyed by articles, prepositions, conjunctions etc.) should be represented as attributes or relations. This criterion is not language-biased: if a given semantic value proves to be conveyed, in any language, by a closed class, it should not be represented as a UW, regardless of its realisation in other languages. The only exception to this principle are the pro-forms, which are represented by a special type of UW, the pro-UW, or null UW (see below).

Compositionality

Simple UWs must correspond to and only to contents expressed by non-compositional lexical items, i.e., words and multiword expressions that cannot be fully reduced to the combination of existing UWs, attributes and relations. Compound and complex UWs must be used when the content can be fully determined by the meanings of constituent expressions and the rules used to combine them.

Comprehensiveness

Universal words are "universal" in the sense that they constitute the lexicon of a "universal language", i.e., that they convey ideas that can be expressed in each and every language. They are not universal in the sense that they are lexicalized in all languages. In that sense, UWs are not to be considered semantic primitives, nor should represent only common concepts. The repertoire of UWs is supposed to be as comprehensive as the set of different individual concepts depicted by different cultures, no matter how specific they are. Furthermore, the lexicon of UNL constitutes an open set, subject to permanent increase with new UWs, as UNL is supposed to incessantly incorporate new cultures and cultural changes.

Universality

Permanent UWs may have different levels of universality and are stored in three nested lexical databases, which are subdivisions of the UNL Dictionary:

• The UNL Core Dictionary contains only permanent simple UWs that are (presumably) shared by all languages
• The UNL Abridged Dictionary contains all permanent UWs (simple, compound or complex) that are shared by at least two different language families
• The UNL Unabridged Dictionary contains all permanent UWs (simple, compound or complex) that are lexicalized in at least one language

Uniqueness

UWs are unique (i.e., non-redundant). There is no synonymy between UWs.

Arbitrariness

Simple UWs are names (and not definitions) for senses. The simple UW does not bring much (or any) information about its sense. It is just a label. Any information concerning the sense is expected to be provided by the three different lexical databases available inside the UNL framework: the UNL Dictionary, the UNL Knowledge Base and the UNL Example Base.

Categories of UWs

Permanent UWs are classified in four different categories, depending on their semantic values:

These categories are semantic rather than syntactic or morphological. They are related to the UWs and are not oriented to any particular language. In that sense, adjectival UWs (such as "300217728" = "delighting the senses or exciting intellectual or emotional admiration") tend to be associated to English adjectives ("beautiful"), but they can also be realised as prepositional phrases ("with beauty"), verbal phrases ("possessing beauty"), etc.

Pro-UWs

The UNL representation is expected to be as semantically saturated as possible, and deictics are supposed to be substituted during the UNLization process. In that sense, ellipses and natural language pro-forms (such as "he", "she", "it", "they" etc.) are expected to be replaced by their corresponding antecedents. In many cases, however, it is not possible to find a substitute for words requiring information that is not available inside natural language texts. In these cases, we use pro-UWs, which are represented by the null UW "00" combined with attributes, when applicable. The main cases are:

• Exophora, which is the reference to something that is not inside the text. This is the case of personal pronouns (such as "I", "you", "we" etc.) for which there is no antecedent in the text (i.e., which refer directly to the context of utterance). These pronouns are represented by the null UW "00" followed by the person attributes (@1, for first person singular; @2, for second person singular; @3, for third person singular; @1.@pl, for first person plural; @2.@pl, for second person plural; and @3.@pl, for third person plural)
• Indefinite pronouns (such as "none", "anyone", "everything" etc.), which refer to general categories of people or things. These pronouns are represented by the null UW "00" followed by determiner attributes ("none" = "00.@no", "anyone" = "00.@any.@person", "everything" = "00.@every.@thing" etc.).
• Interrogative pronouns (such as "who", "whom", "where" etc.), which refer to omitted constituents of the syntactic structure. These pronouns are represented by the null UW "00" followed by the attribute "@wh" ("who" = "00.@wh", "whom" = "00.@wh", "where" = "00.@wh" etc.). The difference between them is determined by the relation in which they appear: "00.@wh" is to be interpreted as "who" when the target argument of an "agt" (agent) relation; as "when" when the target argument of a "tim" (time) relation; as a "where" when the target argument of a "plc" (place) relation; and so on.
• Interjections (such as "Ouch!", "Yeah!", "Shhh!" etc.), when used in isolation to express an emotion or sentiment on the part of the speaker. These UWs are always represented by the null UW "00" followed by an emotional attribute (@anger, @pain etc).
• Ellipses, when cannot be replaced by any antecedent, are represented by the null UW "00" without any specific attribute: "To be or not to be?", for instance, should be represented either as "aoj(exist,00)" or "aoj(00,00)", depending on the interpretation ("to exist or not to exist" or "to be that or not to be that", respectively). because the necessary subject is missing and cannot be linked to any particular referent.

It is important to stress that all cases above refer to situations where the semantic content cannot be fully saturated. Whenever possible, pro-forms and ellipses are expected to be replaced by their referents. For instance, the pro-UW "00.@3" is not supposed to be used in the case of "Peter said that he will not come", if we are sure that "he" is "Peter". In this case, this sentence is expected to be represented as "Peter(i) said that Peter(i) will not come". It should also be stressed that, in the UNL approach, pronouns should be differentiated from determiners. The word "which" in "which is that?" is an interrogative pronoun and should be represented, therefore, by the pro-UW "00.@wh", if we cannot determine to what we are referring to; but the word "which" in "which book is that?" is a determiner, to be represented as an attribute (.@wh) assigned to "book" ("book.@wh").

Formal syntax

The syntax for permanent UWs is defined as follows:

UNL REPRESENTATION
<PERMANENT UW>       ::= <integer>
<TEMPORARY UW>       ::= """<ASCII character>+"""

NL REPRESENTATION
<TEMPORARY UW>       ::= """<UTF-8 character>+"""
<PERMANENT UW>       ::= <root>[<suffix>]
<root>               ::= <UTF-8 character>+
<suffix>             ::= “(“ <suffix> [ “,” <suffix> ]… “)” | <relation> { “>” , “<” } <root>
<relation>           ::= {“agt”, "and", "aoj", ...}

where:
+ to be repeated 1 or more times
< > variable
" " terminal symbol
::= ... is defined as ...
| or
[ ] optional element
{ } alternative element
... to be repeated more than 0 times

FAQs

Proper names are represented as permanent or temporary UWs?

The difference between permanent and temporary UWs has not been staten formally. Most named entities, for instance, are represented as temporary UWs, because it would not be feasible to include them all in the UNL Dictionary. Nevertheless, some named entities of widespread use (such as "England", "William Shakespeare", "Romeo and Juliet", "Romeo" etc) have been already included in the UNL Dictionary and are treated as permanent UWs. Our current criteria is the Wikipedia. If a proper name is defined as an entry in the Wikipedia, then it should be defined as a permanent UW and included in the UNL Unabridged Dictionary.

How to decide whether a concept must be represented as a simple, a compound or a complex UW?

The main criteria is the Principle of Compositionality (Frege's Principle), i.e., that the meaning of a complex expression is determined by the meanings of its constituent expressions and the rules used to combine them. Compound and complex UWs are analytical representations of the meaning structure, and must be used if and only if the meaning of the whole can be derived from the meaning of its parts. Otherwise, you should use simple UWs

In principle, all concepts could be represented in any of these three formats. Consider, for instance, the concept "one who writes", which is lexicalized in English by the word "writer". This concept could be represented in UNL as:

• "writer" (Simple UW), i.e., a single lexical unit;
• "writ.@agent" (Compound UW), i.e., as a simple UW and an attribute corresponding to the morphological structure of the word ("writ+er"); or
• "agt(write,person.@topic)" (Complex UW), i.e., as a UNL graph corresponding to the definition ("one who writes")

These differences do not pose any practical restrictions to the UNL representation. For instance, the English noun phrase "good writer" could be represented in UNL as:

• mod(writer, good) ("one who writes" as a Simple UW)
• mod(writ.@agent, good) ("one who writes" as a Compound UW)
• mod(:01,good)agt:01(write,person.@topic) ("one who writes" as a Complex UW)

In the same way, these differences do not pose any restrictions to the resources (dictionaries and grammars). For instance, the French dictionary could bring :

• [écrivain]{} "writer" (LEX=N,POS=NOU,GEN=MCL,NUM=SNG)<fra,0,0>; ("one who writes" as a Simple UW)
• [écrivain]{} "writ.@agent" (LEX=N,POS=NOU,GEN=MCL,NUM=SNG)<fra,0,0>; ("one who writes" as a Compound UW)
• [écrivain]{} "agt(write,person.@topic)" (LEX=N,POS=NOU,GEN=MCL,NUM=SNG)<fra,0,0>; ("one who writes" as a Complex UW)

But these differences do pose semantic consequences: a simple UW represents a concept seen as a single unit, whereas compound and complex UWs are strictly compositional, i.e., the meaning of the UW is entirely derived from its components. For instance, the word "writer", in English, is normally associated to an occupation. Although this feature ("as an occupation") could be considered taken for granted in the simple UW, it should be made explicit in a compound or a complex UW.