Specs

The UNL Specs define the formal grammar that is used to form UNL sentences and UNL documents. Although the UNL Specs have undergone several changes throughout the history of UNL, there have been many prevailing features, which correspond to the main underlying assumptions on language and knowledge representation under the UNL framework, and which stand for the backbone and the cornerstone of UNL.

The main assumption is that knowledge is declarative. The UNL assumes that human knowledge can be represented as a directed hypergraph, i.e., as an array of two different types of discrete entities: nodes and arcs.

In a UNL graph, the nodes - which are referred to as "Universal Words", or simply "UWs" - play the role of isolated concepts in human cognition. They correspond to relatively stable units of knowledge that can be associated to natural language open lexical categories (noun, verb, adjective and adverb). UWs can be either simple (atomic) or complex (made out of other UWs). In the latter case, they are represented as a hypernode, i.e., as a subhypergraph. UWs have also been claimed to be universal, in the sense they could be expressed by any natural language, either as a single word or as an entire description.

In the UNL framework, there are two possible types of arcs: attributes and relations.

Attributes are arcs linking a node to itself. They correspond to one-place predicates, i.e., functions that take a single argument. They provide transformations on isolated nodes. In UNL, attributes have been normally used to represent information conveyed by natural language grammatical categories (such as tense, mood, aspect, number, etc).

Relations are arcs linking a node to another different node. They are two-place predicates, i.e., functions that take two arguments. They are always binary and directed. In UNL, relations have been normally used to represent semantic (thematic) roles (such as agent, object, instrument, etc) between nodes.

The sets of attributes and relations, which are stated by the Specs, have changed considerably along the years. The set of UWs have also undergone many changes, but this repertoire is actually listed in the UNL Dictionary, which is supposed to be dynamic and permanently open to new additions.

• Version 1.0 (April, 1998)
• Version 1.5 (May, 1998)
• Version 2.0 (July, 1999)
• Version 3.0 (November, 2001)
• Version 3.1 (May, 2002)
• Version 3.2 (July, 2003)
• Version 3.3 (December, 2004)
• Version 2005 (June, 2005)