Grammar

Grammar is the set of logical or structural rules that govern the composition of sentences, phrases and words.

Types of Grammar

In the UNL framework, we distinguish two types of grammar:

• The UNL-NL (Generation) Grammar is used to generate natural language out of UNL
• The NL-UNL (Analysis) Grammar is used to generate UNL out of natural language

Given the issues involved in

• D-rules, or disambiguation rules, are used to assign priorities
• T-rules, or transformation rules, are used to modify structures. T-rules are further divided in:
  • A-rules (affixation rules) apply over isolated word forms (as to generate possible inflections);
  • L-rules (linear rules) apply over lists of word forms (as to provide transformations in the surface structure);
  • S-rules (syntactic rules) apply over trees (as to modify the syntactic configuration).

Examples of Grammar Rules

Type	Rule	Description	Example
D-rule	(ART)(ART)=0;	It's not possible to have an article after another article
A-rule	PLR:=0>"s";	In case of plural (PLR), add "s" to the end of the word	table > tables, boy > boys
L-rule	("I")(BLK)("am"):=("I'm");	In case of "I" before a blank space and "am", replace "I" by "I'm"	I am > I'm
S-rule	MTW:=VA("into account");	In order to form the multiword expression, add "into account" as an adjunct to the verb (VA).	take > take into account

Syntax

D-rules are defined by the general syntax:

<CONDITION> = <PRIORITY>;

While T-rules are defined as:

<CONDITION> := <ACTION>;

Both rules always end in a semicolon (";"). Special symbols and notation apply in each case. For further information, see D-rules, A-rules, L-rules or S-rules.

When to use D-rules

D-rules must be used to assign priorities. They do not provoke any changes, but only induce or prohibit transformations.

When to use T-rules

T-rules are used for changes, and vary according to the scope of the changes:

• A-rules are used when the transformations apply over isolated forms to generate inflections of the base form. They are used only when the transformations may be expressed by prefixation, infixation or suffixation. In any case, the transformation must affect only the structure of the word; the structure of the phrase is preserved. In that sense, A-rules must never be used when a new word is introduced in the syntactic structure (as in the formation of compounds).
• L-rules are used when the transformations affect a linear sequence of isolated forms. The transformations are rather at the surface level and do not affect the deep structure of the phrase.
• S-rules are used when the transformations affect the structure of the phrase, as in the generation of compounds (including compound tenses and periphrastic constructions). They are also used to describe syntactic behaviour such as word order, agreement and government.