Universal Relations

Revision as of 11:35, 28 October 2014

Universal Relations, formerly known as "links", are labelled arcs connecting a node to another node in a UNL graph. They correspond to two-place semantic predicates holding between two Universal Words. In UNL, universal relations have been normally used to represent semantic cases or thematic roles (such as agent, object, instrument, etc.) between UWs. The repertoire of universal relations is defined in the UNL Specs and it is not open to frequent additions.

Definition

In the UNL framework, universal relations describe semantic functions between two UWs. These functions are binary and directed (from a source to a target) and are claimed to be universal. Because of their similarity in name and function to syntactic relations, it may seem that the labels used for relations are different names for special grammatical functions. This is emphatically not the case. The intention is that the labels used denote specific ideas rather than grammatical structures: the idea of “something that initiates an event,” or “agent” for example, is quite different from “grammatical subject of a sentence”, even though many times the subject of a sentence will indicate the agent of the event. The agent of an event may also appear as an adjective or noun modifier, with the preposition “by” or embedded in nouns with “er” suffixes. The whole point of the conceptual relations is to have a name for these very different grammatical structures which are conceptually quite the same. Thus, the conceptual relations used in UNL are much more abstract than the grammatical relations found in sentences.

Syntax

Universal relations are represented as follows:

<rel>:<scope>(<source>;<target>)

where:

• <rel> is the name of the relation (two-character or three-character lower-case strings) (see the complete list of relations below)
• <scope> is the scope of the relation (two-character unique identifier for the scope). The scope may be omitted if the main scope, i.e., :00. See scope.
• <source> is the UW that assigns the relation <rel>
• <target> is the UW that receives the relation <rel>.

Hierarchy of relations

Universal Relations are organized in a hierarchy where lower nodes subsume upper nodes. The topmost level is the relation "rel", which simply indicates that there is a semantic relation between two elements.

Observations

1. Arguments of relations are not commutative:

   cnt(evidence;absence),i.e., evidence of absence, is different from cnt(absence;evidence), i.e., absence of evidence

2. The target always defines the relation:^[1]

   <relation>(<source>;<target>) => <target> is the <relation> of <source>

   • agt(kill;Peter) = Peter is the agent of kill
   • obj(kill;Peter) = Peter is the patient of kill
   • tim(kill;yesterday) = yesterday is the time of kill
   • plc(kill;kicthen) = kitchen is the place of kill
   • mod(book;beautiful) = beautiful is a modifier of book
   • icl(document;book) = book is a type of document
   • iof(city;Paris) = Paris is an instance of city
   • agt:01(kill;Peter) = Peter is the agent of kill in the scope :01 (see scope).

3. Relations describe semantic dependencies rather than syntactic roles.

   The same relation may play different syntactic roles. Consider, for instance, the case of the relation 'gol' (goal):

   • Specifier: Peter received the book = gol(received;Peter)
   • Complement: Mary gave the book to Peter = gol(gave;Peter)
   • Adjunct: Mary bought a book to Peter = gol(bought;Peter)

4. Lexical and syntactic ambiguities are solved through relations.

   Consider, for instance, the case of the English preposition "in", as in Peter works in X.

   • plc(work;X) = X is the physical place where Peter works (as in Peter works in Geneva)
   • lpl(work;X) = X is the logical place where Peter works (as in Peter works in politics)
   • cnt(work;X) = X is the content of the work of Peter (as in Peter works in improving a given technology)
   • tim(work;X) = X is the time when Peter works (as in Peter works in the summer)
   • dur(work;X) = X is the duration of the work of Peter (as in Peter works in ten hours)
   • man(work;X) = X is the manner Peter works (as in Peter works in intervals)

5. Relations are not necessarily bound to a given lexical category.

   The same relation may be used to describe nominal and verbal structures:

   • agt: John arrived = agt(arrived;John), arrival of John = agt(arrival;John)
   • gol: go to NY = gol(go;NY), train to NY = gol(train;NY)
   • cnt: talk about John = cnt(talk;John), book about John = cnt(book;John)

6. In most cases, lower relations may be completely replaced by the corresponding upper levels with the help of attributes:
   • come from NY = src(come;NY) = plc(come;NY.@from)
   • go to NY = gol(go;NY) = plc(go;NY.@to)
   • go through Geneva = via(go;Geneva) = plc(go;Geneva.@through)
   • work since early = tmf(work;early) = tim(work;early.@since)
   • work until late = tmt(work;late) = tim(work;late.@until)
   • work during the summer = dur(work;summer) = tim(work;summer.@during)
   • kill with a knife = ins(kill;knife) = man(kill;knife.@with)
   • etc.
7. In several cases, however, relations are not completely interchangeable, and replacement implies a significant semantic loss. In these cases, upper levels must be used carefully, and only when there is no other alternative:
   • John is Peter = equ(Peter;John) ≈ aoj(Peter;John)
   • Dogs are mammals = icl(mammals;dogs) ≈ aoj(mammals;dogs)
   • John is a human being = iof(human being;John) ≈ aoj(human being;John)
   • table of wood = mat(table;wood) ≈ mod(table;wood)
   • city of New York = nam(city;New York) ≈ mod(city;New York)
   • Peter's book = pos(book;Peter) ≈ mod(book;Peter)
8. The use of relations depends on the internal semantic structure of the UW (see semantic frames).

   Consider, for instance, the verbs "to kill", "to love" and "to give":

   • To kill: the subject is the agent of the action, and the object is the patient, in the sense it is transformed by the action. Therefore, the verb "to kill" assigns the relations "agt" (agent) to its subject and "obj" (patient) to its object.
   • To love: the subject is not properly an agent, in the sense that it does not carry out the event; it is rather an experiencer. Additionally, the object is not a "patient", in the sense that it does not undergo any change; it is actually the content or theme of the event. Therefore: the verb "to love" assigns the relations "exp" (experiencer) to its subject and "cnt" (content) to its object.
   • to give: the subject is the agent of the action, and the verb contains two objects: the object that is given and the recipient of this object. The object that is given normally does not undergo any change other than the position and, in this sense, is normally represented as "cnt" (content); the recipient is represented by the relation "gol" (goal).

List of relations in alphabetical order

Notes

1. ↑ The order of the arguments, in many cases, is counter-intuitive. Consider, for instance, the case of "icl" (hyponymy) as in "Dogs are mammals". The relation is icl(mammal;dogs) because "dogs" is the target of the hyponymy, i.e, "dogs" is a hyponym of "mammals", and not the opposite. This seems to contradict with "Peter is in NY", where we have plc(Peter;NY), but it's important to notice that, in both cases, the general principle of the order (i.e., the relation is always defined by the target) is being followed. In this sense, an important change from the past Specs is the order of the relations "and" and "or". Up to the UNL2005, "Mary and John" were represented as and(John;Mary); from the version UNL2010, the same relation, in order to preserve the general principle of the order, is represented as and(Mary;John).