Relations

In order to form a natural language sentence or a UNL graph, nodes are inter-related by relations. In the UNL framework, there can be three different types of relations:

• the linear relation L expresses the surface structure of natural language sentences
• syntactic relations express the deep (tree) structure of natural language sentences
• semantic relations express the structure of UNL graphs

Properties of relations

The linear relation is always binary and is represented in two possible formats

• L(%x;%y), where L is the invariant name of the linear relation, and %x and %y are nodes; or
• (%x)(%y)

Syntactic relations are not predefined, although we have been using a set of binary relations based on the X-bar theory.

Semantic relations constitute a predefined and closed set that can be found here.

Syntactic and semantic relations are represented in the same way

• rel(%x;%y), where "rel" is the name of the relation, %x is the source node, and %y is the target node

Arguments of linear, syntactic and semantic relations are not commutative.

The order of the elements in a relation affects the result:

(%x)(%y) is different from (%y)(%x)

relation(%x;%y) is different from relation(%y;%x)

Linear and semantic relations are always binary; syntactic relations may be n-ary

L(%x;%y) - linear relation

agt(%x;%y) - semantic relation

VH(%x) - unary syntactic relation

VC(%x;%y) - binary syntactic relation

XX(%x;%y;%z) - possible ternary syntactic relation

Inside each relation, nodes are isolated by semicolon (;).

VC(%x;%y)

VC(%x,%y)

Inside each relation, nodes may be referenced by any of its elements, isolated by comma (,)

("a")([b]) - linear relation between a node where string = "a" and another node where headword = [b]

L([[c]];D) - linear relation between a node where UW = [[c]] and another node having the feature D

VC(%a;%b) - syntactic relation between a node where index = %a and another node where index = %b

agt("a",[a],[[a]],A;"b",[b],[[b]],B) - semantic relation between a node having the feature A where string = "a" AND headword "a" AND UW = [[a]] AND another node having the feature B where string = "b" AND headword = [b] AND UW = [[b]]

Relations may be conjoined through juxtaposition

("a")("b")("c") - two linear relations: one between ("a") and ("b") AND other between ("b") and ("c")

agt(%x;%y)obj(%x;%z) - two semantic relations: one between (%x) and (%y) AND other between (%x) and (%z)

VC([a];[b]),VC([a];[c]) - conjoined relations must not be isolated by comma

Relations may be disjoined through {braces}

{("a")|("b")}("c") - either ("a")("c") or ("b")("c")

{agt(%x;%y)|exp(%x;%y)}obj(%x;%z) - either agt(%x;%y)obj(%x;%z) or exp(%x;%y)obj(%x;%z)

Syntactic and semantic relations may be replaced by regular expressions

/.{2,3}/(%x;%y) - any relation made of two or three characters between %x and %y