Chapter 3  UNL Expressions

3.1 An UNL Expression

Any component such as a word, a phrase or a title and, of course, a sentence of a native language can be represented with UNL expressions. An UNL expression therefore consists of an UW or a (set of) binary relation(s). In the UNL documents, a set of UNL expressions for a setnece is enclosed by the tags {unl} and {/unl} inside [S] and [/S]. In case of an UW, the UW need to be enclosed further by the tags [W] and [/W]. 

3.2 Entry of an UNL Expression

It is essential that one UW is marked with the attribute "@entry" in the UNL expressions of a sentence or a scope. Such marked UW plays two roles: One is to indicate the head or entrance of the semantic network of a set of UNL expressions. The other one is to specify the main or central UW of a sentence or a compound concept.

This section explains which word will be the entry node in various cases.

In a Sentence, basically, the @entry is attached to the UW of the main predicate verb of a sentence, except for the case (2) below, where the @entry is attached to the UW of the complement of the sentence. The followng sre the sentence patterns of English with some examples. In each pattern, the word that its UW should be attached by @entry is shown in bold.

(1) S V_intens A_place

Mary is (UW=exist.@entry) in the house.

(2) S V_intens C_s

Mary is kind (@entry).
Mary is a nurse (@entry).

(3) S V_monotrans O_d

Somebody caught (@entry) the ball.

(4) S V_{complex trans} O_d A_place

I put (@entry) the plate on the table.

(5) S V_{complex trans} O_d C_o

We have proved (@entry) it wrong.

(6) S V_ditrans O_i O_d

He gives (@entry) me a present.

(7) S V_intrans

He laughed (@entry).  

In case of a Compound Word, when an UNL expression consists of a compound word, the @entry is always attached to the UW of its main or central word.  

In case of a Word, the @entry is attached to the UW of the word when the UNL expression consists of only a single UW.

In case of a Scope, it is essential that one UW must be marked with @entry. Which UW should be attached with the @entry in a scope is explained in the next section “3.3 Scope” in detail.  

Because of the role of the @entry, same UNL expressions can express different meanings according to which UW the @entry is attached to. For instance, in the sentence

“The budget is for food”,

the @entry will be attached to the UW of food. But for the sentence

“The budget for food”,

the @entry will be attached to the UW of budget. Although these two sentences have the same binary relations as shown in UNL1 and UNL2 below.

3.3 Scope

As explained earlier, a compound concept (UW) in a sentence can be expressed as a scope. This is the main case of using a scope. A scope may also be used for expressing Coordinating Concepts. 

In order to avoid redundancy, there are two rules need to be followed when making a scope:

1.          If a scope itself is not linked with any other UWs included in the sentence, this scope is not necessary but redundant. A redundant scope should not be made.

2.          It is not allowed to link the entry-UW (the UW marked with @entry) of a scope with any UWs outside the scope directly. Since the entry-UW of a scope plays the same role as the whole scope itself in an UNL expression, any links to the entry-UW should be linked to the whole scope.

Sometimes, it is possible to link the main UW of a compound UW with others directly instead of making a scope for the compound UW. For instance this happens when the object of a sentence is also the subject of its sub-sentence. The following shows an example of this case.

 The sentence "I know the lady who is talking there" can be expressed using or without a scope, as shown in UNL1 and UNL2 below.

 Example 1

The underlined part is the focused part in the above example. In the first UNL expression UNL1, the UW of “the lady" is linked by both "know" and “talk” directly, and no scope is used. In the second one UNL2 “the lady who is talking there” is treated as a scope with “the lady” as the entry-node, which is linked with “know”. Both UNL expressions are considered as correct.

This can also be said to the case of sentence like "I think it is new". Its UNL expressions are shown below.

Example 2

3.3.1 A Compound Concept 

The underlined part in the sentence “He asked us to leave the room” can be considered as a kind of Compound UW. Using a scope for the compound UW, its UNL expression will be as UNL1 shows. This sentence is also allowed not to use a scope as UNL2 shows.

 Example 1

In case of the sentence “Women who wear big hats in movie theaters should be asked to leave”, the underlined part can be treated as a scope and its UNL expressions is shown in UNL1. The same UNL 2 shows the other UNL expressions without a scope.

Example 2

A correction:

The corresponding UNL expressions for the above sentence in the book “A Gift for a Millennium” on page 21 has two mistakes: one is that @entry is omitted in the Compound UW expression, the other one is that the relation between UW “ask” and the scope should be "gol" not "agt". And there must be link “agt” between “leave” and “woman” or the scope, in which the “woman” is the entry-node. 

3.3.2 Coordinating Concepts

A set of UWs which are connected by "and” or “or” can be expressed with a scope. 

Below is the UNL expression of the sentence "There is a boy and two girls, the boy is naughty and the girls are cute." This UNL expression is a little bit complicated. In it, the part of "a boy and two girls" is expressed in a scope, this makes it easier to connecte this part with "there is (UW=exist)". The two UWs "girl" and "boy" inside the scope are also linked from the nodes “cute” and “naught” outside of the scope respectively. 

Example

In the previous version of the UNL Manual, the relation “obj” was used between “exist” and the scope :01 in the above example. As both the UW and KB systems are improved, the characteristic of the UW “exist” became clear about what kind of relations it takes. As a result, the “exist” is considered to belong to the “state verbs” and takes the relation “aoj” only differing from the other kind of “state vers” like “know”, which also takes the relation “obj” as in “I know it”.  

and:01 ( girl.@pl.@entry, boy.@indef )

shows the relation between the nodes "girl" and "boy” inside the scope 01. “@pl.@entry” are the attributes of “girl”, “@indef” is an attribute of “boy”, and all of them have label 01.

aoj ( naughty, boy.@def )

shows the relation between "naughty" and “boy” of the main sentence. “@def” is an attribute of “boy”, it has level 00.

aoj ( cute.@entry, girl.@pl.@def )

shows the relation between "cute" and “girl” of the main sentence. “@entry” is the attribute of “cute”, “@pl.@def” are the attributes of “boy”, all the attributes have label 00.

Figure 1: A scope example of coordinating concepts

Explanations of UWs, identifiers of UW (UW-IDs), Relations and Attributes

An UW with an identifier (so-called UW-ID) defines a node in an UNL expression. Same UW with same UW-ID defines the same node, and it is global. A node defined by such UWs and UW-IDs in a scope can be linked with other nodes from other scopes and the main sentence. UW-IDs have the default value 00 when it is not indicated.

Relations and Attributes are always local. It means that each relation and attribute can only be referred to in one scope or the main sentence. Every relation and attribute are also given an identifier, with the same value as the scope or the main sentence it belongs to. The identifiers for the relations and attributes that belong to the main sentence always have the value 00. Therefore, any scopes else in a sentence cannot use the value 00 as identifiers. The EnConverter generates identifiers for the scopes starting from the value 01.