Grammar Specs

Revision as of 22:52, 17 April 2009

UNL-NL grammars are sets of rules for translating UNL expressions into natural language (NL) sentences and NL sentences into UNL expressions. They are normally unidirectional, i.e., the enconversion grammar (NL-to-UNL) is different from the deconversion grammar (UNL-to-NL), even though they share the same basic syntax. In order to standardize the language resources in the UNL framework, the UNDL Foundation recommends the adoption of the following specifications for both UNL-to-NL and NL-to-UNL grammars. This formalism, however, is not supported by the UNL Centre's tools, and it is only required by those interested in using UNDL Foundation's tools.

Types of rules

In the UNL Grammar there are two basic types of rules:

Transformation rules

Used to generate natural language sentences out of UNL graphs and vice-versa.

Disambiguation rules

Used to improve the performance of transformation rules by constraining their applicability.

The Transformation 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.

The Disambiguation Rules, which were directly inspired by the UNL Centre's former co-occurrence dictionary and knowledge base, follows a slightly different formalism:

α=P;

where the left side α is a statement and the right side P is an integer from 0 to 255 that indicates the probability of occurrence of α.

We present both types of rules and their role in the UNL System. We introduce, first, the basic symbols that are used both by transformation and disambiguation rules; next, we present the transformation rules and their several subtypes; and finally we present the disambiguation rules.

Basic symbols

Both transformation and disambiguation rules use the same set of basic symbols:

The following symbols are related to the structure of the UNL Dictionary, as illustrated below:

[NLW] {} “UW” (aa=AA, bb=BB, …) <L,F,P>;

[book] {} “book(icl>document)” (pos=NOU) <EN,0,0>;

[foot] {} “foot(icl>vertebrate foot) (pl=”feet”) <EN,0,0>;

[baby] {} “baby(icl>child) (pl=”y”>”ies”) <EN,0,0>;

[[bring] [back]] {} “to bring back(icl>to bring) (pos=VER) <EN,0,0>;