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| | | #REDIRECT [[Grammar Specs]] |
| == Basic concepts ==
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| ;[[Node]]
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| :A node is the most elementary unit in the graph. It is the result of the [[tokenization]] process, and corresponds to the notion of "lexical item". At the surface level, a natural language sentence is considered a list of nodes, and a UNL graph a set of relations between nodes.
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| ;[[Relation]]
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| :In order to form a natural language sentence or a UNL graph, nodes are inter-related by relations. In the UNL framework, there can be three different types of relations: linear, syntactic or semantic.
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| ;[[Hyper-Node]]
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| :A hyper-node is a sub-graph, i.e., a node containing relations between nodes.
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| ;[[Hyper-Relation]]
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| :A hyper-relation is a relation between relations.
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| == Basic symbols ==
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| {| border="1" cellpadding="2" align=center
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| |+Basic symbols used in UNL grammar rules
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| !Symbol
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| !Definition
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| !Example
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| |-
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| |align=center|<nowiki>^</nowiki>
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| |not
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| |^a = not a
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| |-
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| |align=center|{ | }
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| |or
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| |<nowiki>{a|b}</nowiki> = a or b
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| |-
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| |align=center|%
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| |index for nodes, attributes and values
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| |%x (see [[#Indexes|below]])
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| |-
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| |align=center|#
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| |index for sub-NLWs
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| |#01 (see [[#Indexes|below]])
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| |-
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| |align=center|=
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| |attribute-value assignment
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| |POS=NOU
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| |-
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| |align=center|!
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| |rule trigger
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| |!PLR
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| |-
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| |align=center|&
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| |merge operator
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| |%x&%y
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| |-
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| |align=center|?
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| |dictionary lookup operator
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| |?[a]
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| |-
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| |align=center|“ “
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| |string
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| |"went"
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| |-
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| |align=center|[ ]
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| |natural language entry (headword)
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| |[go]
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| |-
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| |align=center|[[ ]]
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| |UW
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| |[[to go(icl>to move)]]
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| |-
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| |align=center|( )
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| |node
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| |(a)
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| |-
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| |align=center|//
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| |regular expression
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| |/a{2,3}/ = aa,aaa
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| |}
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| ;The differences between "", [] and [[]]
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| :Double quotes are always used to represent strings: "a" will match only the string "a"
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| :Simple square brackets are always used to represent natural language entries (headwords) in the dictionary: [a] will match the node associated to the entry [a] retrieved from the dictionary, no matter its current realization, which may be affected by other rules (the original [a] may have been replaced, for instance, by "b", but will still be indexed to the entry [a])
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| :Double square brackets are always used to represent UWs: <nowiki>[[a]]</nowiki> will match the node associated to the UW <nowiki>[[a]]</nowiki>
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| ;Predefined values (assigned by default)
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| :SCOPE - Scope
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| :SHEAD - Sentence head (the beginning of a sentence)
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| :STAIL - Sentence tail (the end of a sentence)
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| :CHEAD - Scope head (the beginning of a scope)
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| :CTAIL - Scope tail (the end of a scope)
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| :TEMP - Temporary entry (entry not found in the dictionary)
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| :DIGIT - Any sequence of digits (i.e.: 0,1,2,3,4,5,6,7,8,9)
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