Lexica

The UNL framework contains three different types of lexical databases: UNL-only, NL-only and UNL-NL.

UNL

The UNL lexical databases are the following:

• The UNL Dictionary, or simply UNL^dic, is a flat list of UW's and their semantic features
• The UNL Knowledge Base, or simply UNL^kb, is a network with systematic relations between UW's
• The UNL Example Base, or simply UNL^eb, is a network with any relations between UW's

These three databases are nested. The UNL^dic contains UW's and their basic semantic features (such as the information that the UW corresponding to "table" is a nominal concrete concept that belongs to the class of artifacts). The UNL^kb contains the UNL^dic and the set of relations that are necessary to define a UW (such as the information that "table" is a piece of furniture with vertical legs and a flat horizontal surface). The UNL^eb contains the UNL^kb and the set of relations that are often found between UW's (such as the information that tables are normally round or square, that are made of hard materials, etc.). In general, the difference between the UNL^kb and the UNL^eb is that the former is dictionary-based (i.e., it tries to represent the information that is normally ascribed in the definitions provided by dictionaries) whereas the latter is corpus-based (i.e., it tries to represent the concept as it appears in the corpus).

NL

• The NL Dictionary, or simply NL^dic, is a list of natural language entries with the corresponding morphological and syntactic features (such as part of speech, gender, number, case, subcategorization frame, etc.).

UNL-NL

• The UNL-NL Dictionary, or simply UNL-NL^dic, is list of systematic lexical mappings between UW's and natural language entries
• The UNL-NL Memory, or UNL Memory Base, or simply UNL-NL^MB, is a list of mappings between UNL and a given natural language

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.