Universal Networking Language (UNL) is a declarative formal language specifically designed to represent semantic data extracted from natural language texts. It can be used as a pivot language in interlingual machine translation systems or as a knowledge representation language in information retrieval applications.
Scope and goals
UNL
is designed to establish a simple foundation for representing the most
central aspects of information and meaning in a machine- and
human-language-independent form. As a language-independent formalism,
UNL aims to code, store, disseminate and retrieve information
independently of the original language in which it was expressed. In
this sense, UNL seeks to provide tools for overcoming the language
barrier in a systematic way.
At first glance, UNL seems to be a kind of interlingua, into
which source texts are converted before being translated into target
languages. It can, in fact, be used for this purpose, and very
efficiently, too. However, its real strength is knowledge representation
and its primary objective is to provide an infrastructure for handling
knowledge that already exists or can exist in any given language.
Nevertheless, it is important to note that at present it would be
foolish to claim to represent the “full” meaning of any word, sentence,
or text for any language. Subtleties of intention and interpretation
make the “full meaning,” however we might conceive it, too variable and
subjective for any systematic treatment. Thus UNL avoids the pitfalls
of trying to represent the “full meaning” of sentences or texts,
targeting instead the “core” or “consensual” meaning most often
attributed to them. In this sense, much of the subtlety of poetry,
metaphor, figurative language, innuendo, and other complex, indirect
communicative behaviors is beyond the current scope and goals of UNL.
Instead, UNL targets direct communicative behavior and literal meaning
as a tangible, concrete basis for most human communication in practical,
day-to-day settings.
Structure
In
the UNL approach, information conveyed by natural language is
represented sentence by sentence as a hypergraph composed of a set of
directed binary labeled links (referred to as relations) between nodes or hypernodes (the Universal Words, or simply UWs), which stand for concepts. UWs can also be annotated with attributes representing context information.
As an example, the English sentence ‘The sky was blue?!’ can be represented in UNL as follows:
In the example above, "sky(icl>natural world)" and
"blue(icl>color)", which represent individual concepts, are UWs;
"aoj" (= attribute of an object) is a directed binary semantic relation
linking the two UWs; and "@def", "@interrogative", "@past",
"@exclamation" and "@entry" are attributes modifying UWs.
UWs are intended to represent universal concepts, but are
expressed in English words or in any other natural language in order to
be humanly readable. They consist of a "headword" (the UW root) and a
"constraint list" (the UW suffix between parentheses), where the
constraints are used to disambiguate the general concept conveyed by the
headword. The set of UWs is organized in the UNL Ontology, in which
high-level concepts are related to lower-level ones through the
relations "icl" (= is a kind of), "iof" (= is an instance of) and "equ"
(= is equal to).
Relations are intended to represent semantic links between words
in every existing language. They can be ontological (such as "icl" and
"iof," referred to above), logical (such as "and" and "or"), and
thematic (such as "agt" = agent, "ins" = instrument, "tim" = time, "plc"
= place, etc.). There are currently 46 relations in the UNL Specs. They
jointly define the UNL syntax.
Attributes represent information that cannot be conveyed by UWs
and relations. Normally, they represent information concerning time
("@past", "@future", etc.), reference ("@def", "@indef", etc.), modality
("@can", "@must", etc.), focus ("@topic", "@focus", etc.), and so on.
Within the UNL Program, the process of representing natural language sentences in UNL graphs is called UNLization, and the process of generating natural language sentences out of UNL graphs is called NLization.
UNLization, which involves natural language analysis and understanding,
is intended to be carried out semi-automatically (i.e., by humans with
computer aids); and NLization is intended to be carried out fully
automatically.
History
The UNL Programme started in 1996, as an initiative of the Institute of Advanced Studies of the United Nations University
in Tokyo, Japan. In January 2001, the United Nations University set up
an autonomous organization, the UNDL Foundation, to be responsible for
the development and management of the UNL Programme. The foundation, a
non-profit international organisation, has an independent identity from
the United Nations University, although it has special links with the
UN. It inherited from the UNU/IAS the mandate of implementing the UNL
Programme so that it can fulfil its mission.
The programme has already crossed important milestones. The
overall architecture of the UNL System has been developed with a set of
basic software and tools necessary for its functioning. These are being
tested and improved. A vast amount of linguistic resources from the
various native languages already under development, as well as from the
UNL expression, has been accumulated in the last few years. Moreover,
the technical infrastructure for expanding these resources is already in
place, thus facilitating the participation of many more languages in
the UNL system from now on. A growing number of scientific papers and
academic dissertations on the UNL are being published every year.
The most visible accomplishment so far is the recognition by the
Patent Co-operation Treaty (PCT) of the innovative character and
industrial applicability of the UNL, which was obtained in May 2002
through the World Intellectual Property Organisation (WIPO). Acquiring
the patents (US patents 6,704,700 and 7,107,206) for the UNL is a
completely novel achievement within the United Nations.
