Lexica

The UNL System contains three different types of lexical databases: dictionaries, knowledge base and example bases.

Dictionaries

Main article: Dictionary Specs

In the UNL System, a dictionary is a flat list of entries with their corresponding features. The dictionaries comply with the structure defined in the Dictionary Specs and must contain only tags defined in the Tagset. They are divided in three different categories:

• The UNL Dictionary, or simply UNL^dic, is a list of UW's and their semantic (language-independent) features
• The NL Dictionary, or simply NL^dic, is a list of natural language entries with the corresponding morphological and syntactic (language-dependent) features
• The UNL-NL Dictionary, or simply UNL-NL^dic, is list of lexical mappings between UW's and natural language entries

The UNL Dictionary and the NL Dictionary are monolingual databases, whose entries are interlinked by the UNL-NL Dictionary, which brings the mappings between UW's and natural language entries, whenever available. These three dictionaries are normally made through the UNLarium in different steps and constitute the basic resource for UNLization and NLization.

UNL Knowledge Base (UNL^KB)

Main article: UNL Knowledge Base

The UNL Dictionary is simply a flat list of UW's and their corresponding classifiers (such as lexical category, semantic class, abstractness, cardinality, etc.). The UNL Dictionary does not contain any distinguisher, i.e., any information that can be used to differentiate a given UW from the others that belong to the same class. This information is provided in the UNL Knowledge Base, or UNL^KB, which is a semantic network made of relations that are necessary to define UW's.

Consider, for instance, the case of the UW corresponding to the concept "a piece of furniture having a smooth flat top that is usually supported by one or more vertical legs", which may be conveyed by the English word "table". The UNL Dictionary brings only the information that "table" is a nominal concrete concept which belongs to the class of artifacts. The information that "table" is "a piece of furniture having a smooth flat top" is stated in the UNL^KB, where the UW corresponding to "table" is linked to several other UW's (such as "furniture", "smooth flat top", etc.), in order to precise its meaning.

Example Bases

In the UNL System, there are two different types of example bases:

• The UNL Example Base, or simply UNL^EB, is a network with frequent relations between UW's
• The UNL-NL Memory, or UNL Memory Base, or simply UNL-NL^MB, is a list of frequent mappings between UNL and a given natural language

The UNL^EB is a monolingual resource and subsumes the UNL^KB. The difference is that the UNL^KB contains only necessary relations between UW's, whereas the UNL^EB, which is corpus-based, brings any frequent relation between UW's. For instance, the idea that a "table" is "supported by one or more vertical legs" is not represented in the UNL^KB because it is not supposed to be necessary (there are tables that are not supported by legs). This information, as the information that tables are normally round or square, that they are made of hard materials, etc., is repesented in the UNL^EB. The UNL^EB extends and complements the UNL^KB.

The UNL^MB is a bilingual database. The main difference between the UNL-NL^dic and the UNL-NL^MB is that the former involves only lexical units (i.e., entries defined as such in the UNL and the NL dictionaries) whereas the latter involves translation units, which may include several lexical units.