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|  | The following Grammar Specs are used for writing rules for the UNDL Foundation tools ([[IAN]], [[EUGENE]], [[SEAN]], [[NORMA]], etc.).
 |  | #REDIRECT [[Grammar]] | 
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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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|  |   |  | 
|  | == 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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