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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 supposedintended to represent universal concepts, whichbut 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 latterconstraints beingare used to disambiguate the general concept conveyed by the formerheadword. The set of UWs areis organized in the [[UNL Ontology]], wherein upperwhich high-level concepts are usedrelated to disambiguate the lower-level ones through the relations "icl" (= is a kind of), "iof" (= is an instance of) and "equ" (= is equal to) relations.
Relations are expectedintended 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,. andThey theyjointly define the UNL syntax of UNL.
Attributes represent information that cannot be conveyed by UWs and relations. Normally, they represent information onconcerning tense (".@past", "@future", etc.), reference ("@def", "@indef", etc.), modality ("@can", "@must", etc.), focus ("@topic", "@focus", etc.), and so on.
UnderWithin the UNL Program, the process of representing natural language sentences in UNL graphs is called '''enconverting''', and the process of generating natural language sentences out of UNL graphs is called '''deconverting'''. The formerEnconversion, which involves natural language analysis and understanding, is supposedintended to be carried out semi-automatically (i.e., inby ahumans with computer-aided human basisaids); theand latterdeconversion is expectedintended to be donecarried out fully automatically.
== History ==
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