Universal Relations

Revision as of 17:59, 10 September 2013

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>.

Examples

• 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).

Observations

1. Arguments of relations are not commutative:

   mod(evidence,absence) is different from mod(absence,evidence)

2. The <target> defines the relation, i.e., <target> is <rel> of <source> in <scope>

   mod(evidence,absence) = absence is the modifier of evidence, i.e., evidence of absence

   mod(absence,evidence) = evidence is the modifier of absence, i.e., absence of evidence

Use of Universal Relations

Universal Relations are always used to describe semantic dependencies between syntactic constituents. In general, the following applies:

Hierarchy of Universal 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 relation between two elements. The following level brings four general relations: participant (ptp), for the necessary arguments (subject and complements) of verbal predicates; attribute (aoj), for the necessary arguments (subject and complement) of nominal predicates; specifier (mod), for general specifiers; and adjunct (adj), for general adjuncts, including time, location and manner.

List of Universal Relations in alphabetical order

The set of relations has been undergoing some changes throughout the history of UNL. The table below presents the list of relations according to the several UNL Specs.