N-rule

Normalization rules are used to prepare the natural language input for automatic processing. They constitute the preprocessing module that applies over the input as a string and runs prior to the tokenization. The set of n-rules forms the Normalization Grammar, or N-Grammar.

Syntax

Normalization Rules follow the very general formalism

α:=β;

where the left side α is a condition statement, and the right side β is an action to be performed over α.

Roles of Normalization Rules

Normalization rules have two roles:

• to normalize the input text (to replace abbreviations by their extend forms, to extend contractions, etc.)
• to segment the natural language text into sentences (i.e., to create the tags <SHEAD> (beginning of a sentence), <STAIL> (end of a sentence), <CHEAD> (beginning of a scope) and <CTAIL> (end of a scope) inside the input text). These tags are used as sentence and clause boundaries, and define the units of processing of the Transformation and Disambiguation grammars.

Type of Normalization Rules

Normalization rules are string replacement rules. They are used to replace existing strings by new strings. They constitute the preprocessing module of natural language analysis, and apply prior to the tokenization and to any dictionary search, when no attribute other than string itself is available. The string to be replaced may be referred by a constant (between "double quotes") or by a regular expression (between /forward slashes/).

LL rules

ACTION	RULE	DESCRIPTION	EXAMPLE
REPLACE	("source string"):=("target string");	All the instances of the source string will be replaced by the target string	("x"):=("y"); axbxcxd will become aybycyd
APPEND (RIGHT)	("source string",%x):=(%x)(%y,"target string");	The target string will be appended to the right of all instances of the source string.	("x",%x):=(%x)("y",%y); axbxcxd will become axybxycxyd
APPEND (LEFT)	("source string",%x):=(%y,"target string")(%x);	The target string will be appended to the left of all instances of the source string.	("x",%x):=("y",%y)(%x); axbxcxd will become ayxbyxcyxd
DELETE	("source string"):=;	All the instances of the source string will be deleted.	("x"):=; axbxcxd will become abcd

Indexes (%x, %y, etc.) are used in appending rules in order to define the direction (to the left or to the right).

Segmentation

In the UNL framework, natural language segmentation is done through the following tags:

• <SHEAD> indicates the beginning of a sentence
• <STAIL> indicates the end of a sentence
• <CHEAD> indicates the beginning of a scope (any portion of text smaller than a sentence)
• <CTAIL> indicates the beginning of a scope (any portion of text smaller than a sentence)

The tags <SHEAD> and <STAIL> defines the sentence boundaries and are automatically assigned by the system according to line breaks and paragraph breaks. No punctuation sign is used as a sentence boundary by default. In order to break the input text into other portions, the corresponding N-rules must be provided. This is done by appending empty nodes with the features SHEAD, STAIL, CHEAD or CTAIL to the left or to the right of existing strings.

• Original text: <SHEAD>abcde<STAIL>
• Rule: ("c",%x):=(%x)(STAIL);
• Modified text: <SHEAD>abc<STAIL><SHEAD>de<STAIL>

Observations

• The tag <SHEAD> is assigned automatically after the beginning of any new line or paragraph
• The tag <STAIL> is assigned automatically before the beginning of any new line or paragraph
• No punctuation signs are used as sentence boundaries by default (i.e., it is necessary to create N-rules in order to make them sentence boundaries).

Examples of Normalization rules

• Segmentation
  • ("/.*\./",%x):=(%x)(+STAIL,%y); (creates an STAIL node after any sequence of characters followed by "." (/.*\./);
  • ("/\(/",%x):=(+CHEAD,%y)(%x); (creates an CHEAD node before the opening of a parentheses (/\(/);
• Normalization
  • ("an "):=("a "); ("an apple" > "a apple")
  • ("don't"):=("do not"); ("I don't see" > "I do not see")