Grammar

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In the UNL framework, a '''grammar''' is a set of rules that are used to generate UNL out of natural language, and natural language out of UNL. Along with the [[Lexica|UNL-NL dictionaries]], they constitute the basic resource for [[UNLization]] and [[NLization]].
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In the UNL framework, a '''grammar''' is a set of rules that is used to generate UNL out of natural language, and natural language out of UNL. Along with [[Dictionary|dictionaries]], they constitute the basic resource for [[UNLization]] and [[NLization]].
  
== Networks, Trees and Lists ==
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== Basic Symbols ==
Natural language sentences and UNL graphs are supposed to convey the same amount of information in different structures: whereas the former arranges data as an ordered list of words, the latter organizes it as a network. In that sense, going from natural language into UNL and from UNL into natural language is ultimately a matter of transforming lists into networks and vice-versa.
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{{:Basic Symbols}}
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The UNL framework assumes that such transformation can be carried out progressively, i.e., through a transitional data structure: the tree, which could be used as an interface between lists and networks. Accordingly, there are seven different types of rules (LL, TT, NN, LT, TL, TN, NT), as indicated below:
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*'''ANALYSIS''' (NL-UNL)
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== Basic Concepts ==
**LL - List Processing (list-to-list)
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{{:Grammar units}}
**LT - Surface-Structure Formation (list-to-tree)
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**TT - Syntactic Processing (tree-to-tree)
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**TN - Deep-Structure Formation (tree-to-network)
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**NN - Semantic Processing (network-to-network)
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*'''GENERATION''' (UNL-NL)
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== Rules ==
**NN - Semantic Processing (network-to-network)
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{{:Rule}}
**NT - Deep-Structure Formation (network-to-tree)
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**TT - Syntactic Processing (tree-to-tree)
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**TL - Surface-Structure Formation (tree-to-list)
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**LL - List Processing (list-to-list)
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The '''NL original sentence''' is supposed to be preprocessed, by the LL rules, in order to become an ordered list. Next, the resulting '''list structure''' is parsed with the LT rules, so as to unveil its '''surface syntactic structure''', which is already a tree. The tree structure is further processed by the TT rules in order to expose its inner organization, the '''deep syntactic structure''', which is supposed to be more suitable to the semantic interpretation. Then, this deep syntactic structure is projected into a semantic network by the TN rules. The resultant '''semantic network''' is then post-edited by the NN rules in order to comply with UNL standards and generate the '''UNL Graph'''.
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== Modules ==
 
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In the UNL framework there are three types of grammar:
The reverse process is carried out during natural language generation. The '''UNL graph''' is preprocessed by the NN rules in order to become a more easily tractable semantic network. The resulting '''network structure''' is converted, by the NT rules, into a syntactic structure, which is still distant from the surface structure, as it is directly derived from the semantic arrangement. This '''deep syntactic structure''' is subsequently transformed into a '''surface syntactic structure''' by the TT rules. The surface syntactic structure undergoes many other changes according to the TL rules, which generate a NL-like '''list structure'''. This list structure is finally realized as a '''natural language sentence''' by the LL rules.
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*[[N-Grammar]], or Normalization Grammar, is a set of T-rules used to segment the natural language text into sentences and to prepare the input for processing.
 
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*[[T-Grammar]], or Transformation Grammar, is a set of T-rules used to transform natural language into UNL or UNL into natural language.
As sentences are complex structures that may contain nested or embedded phrases, both the analysis and the generation processes may be '''interleaved''' rather than pipelined. This means that the natural flow described above is only "normal" and not "necessary". During natural language generation, a LL rule may apply prior to a TT rule, or a NN rule may be applied after a TL rule. Rules are recursive and must be applied in the order defined in the grammar as long as their conditions are true, regardless of the state.
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*[[D-Grammar]], or Disambiguation Grammar, is a set of D-rules used to to improve the performance of transformation rules by constraining or forcing their applicability.
 
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== Types of rules ==
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''Main article: [[Grammar Specs]]''
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In the UNL framework there are two basic types of rules:
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*Transformation rules, or [[T-rule]]s, are used to manipulate data structures, i.e., to transform lists into trees, trees into lists, trees into networks, networks into trees, etc. They follow the very general formalism
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α:=β;
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where the left side α is a condition statement, and the right side β is an action to be performed over α.  
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*Disambiguation rules, or [[D-rule]]s, are used to improve the performance of transformation rules by constraining or forcing their applicability. The Disambiguation Rules follows the formalism:
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α=P;
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where the left side α is a statement and the right side P is an integer from 0 to 255 that indicates the probability of occurrence of α. 
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== Direction ==
 
== Direction ==
 
In the UNL framework, grammars are not bidirectional, although they share the same syntax:
 
In the UNL framework, grammars are not bidirectional, although they share the same syntax:
*UNL-NL T-Grammar: used for natural language generation
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*[[UNLization]] (NL>UNL)
*UNL-NL D-Grammar: used for improving the results of the UNL-NL T-Grammar
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**The '''N-Grammar''' contains the normalization rules for natural natural analysis
*NL-UNL T-Grammar: used for natural language analysis
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**The '''Analysis T-Grammar''' contains the transformation rules used for natural language analysis
*NL-UNL D-Grammar: used for tokenization and for improving the results of the NL-UNL T-Grammar
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**The '''Analysis D-Grammar''' contains the disambiguation rules used for [[tokenization]] and for improving the results of the NL-UNL T-Grammar
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*[[NLization]] (UNL>NL)
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**The '''Generation T-Grammar''' contains the transformation rules used for natural language generation
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**The '''Generation D-Grammar''' contains the disambiguation rules used for improving the results of the UNL-NL T-Grammar
  
== Units ==
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== Processing Units ==
 
In the UNL framework, grammars may target different processing units:
 
In the UNL framework, grammars may target different processing units:
*'''Text-driven grammars''' operate over texts and process the source document as a single unit
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*'''Text-driven grammars''' process the source document as a single unit (i.e., without any internal subdivision)
*'''Sentence-driven grammars''' operate over sentences and process each sentence or graph separately
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*'''Sentence-driven grammars''' process each sentence or graph separately
*'''Word-driven grammars''' operate over words and process each word or node separately
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*'''Word-driven grammars''' process words in isolation
 
Text-driven grammars are normally used in summarization and simplification, when the rhetorical structure of the source document is important. Sentence-driven grammars are used mostly in translation, when the source document can be treated as a list of non-semantically related units, to be processed one at a time. Word-driven grammars are used in information retrieval and opinion mining, when each word or node can be treated in isolation. <br />
 
Text-driven grammars are normally used in summarization and simplification, when the rhetorical structure of the source document is important. Sentence-driven grammars are used mostly in translation, when the source document can be treated as a list of non-semantically related units, to be processed one at a time. Word-driven grammars are used in information retrieval and opinion mining, when each word or node can be treated in isolation. <br />
All these grammars share the same type of rule.
 
  
 
== Recall ==  
 
== Recall ==  
 
Grammars may target the whole source document or only parts of it (e.g. main clauses):
 
Grammars may target the whole source document or only parts of it (e.g. main clauses):
*Chunk grammars target only a part of the source document
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*'''Chunk grammars''' target only a part of the source document
*Full grammars target the whole source document
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*'''Full grammars''' target the whole source document
  
 
== Precision ==
 
== Precision ==
 
Grammars may target the deep or the surface structure of the source document:
 
Grammars may target the deep or the surface structure of the source document:
*Deep grammars focus on the deep dependency relations of the source document
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*'''Deep grammars''' focus on the deep dependency relations of the source document and normally have three levels (network, tree and list)
*Shallow grammars focus only on the surface dependency relations of the source document
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*'''Shallow grammars''' focus only on the surface dependency relations of the source document and normally have only two levels (network and list)
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== Assessment ==
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''Main article: [[F-measure]]''
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Grammars are evaluated through a weighted average of precision and recall, the F-measure.

Latest revision as of 09:39, 27 May 2014

In the UNL framework, a grammar is a set of rules that is used to generate UNL out of natural language, and natural language out of UNL. Along with dictionaries, they constitute the basic resource for UNLization and NLization.

Contents

Basic Symbols

Basic symbols used in the UNL framework
Symbol Definition Example
( ) node (%a)
" " string "went"
[ ] natural language entry (headword) [go]
[[ ]] UW [[to go(icl>to move)]]
// regular expression /a{2,3}/ = aa,aaa
rel(x;y) relation agt(kill;Peter)
^ not ^a = not a
{ | } or {a|b} = a or b
% index for nodes, attributes and values %x
: scope ID :01
# index for sub-NLWs #01
= attribute-value assignment POS=NOU
! rule trigger !PLR
& merge operator %x&%y
? dictionary lookup operator ?[a]

Basic Concepts

Grammar.png
Node
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.
Relation
In order to form a natural language sentence or a UNL graph, nodes are inter-related by relations. In the UNL framework, there are three different types of relations: the linear (list) relation, syntactic relations and semantic relations.
Hyper-Node
A hyper-node is a sub-graph, i.e., a scope: a node containing relations between nodes.
Hyper-Relation
A hyper-relation is a relation between relations.

Rules

Grammars are sets of rules used to go from UNL into natural language, or from natural language into UNL. In the UNL framework, there can be two different types of rules:

  • T-rules, or transformation rules, are used to perform changes to nodes or relations
  • D-rules, or disambiguation rules, are used to control changes over nodes or relations

T-rules

main article:T-rule

T-rules are used to perform actions and follow the very general formalism

α:=β;

where the left side α is a condition statement, and the right side β is an action to be performed over α.

There are several different especial types of T-rules:

  • A-rule is a specific type of T-rule used for affixation (prefixation, infixation, suffixation)
  • C-rule is a specific type of T-rule used for composition (word formation in case of compounds and multiword expressions)
  • L-rule is a specific type of T-rule used for handling word order
  • N-rule is a specific type of T-rule used for segmenting sentences and normalizing the input text
  • S-rule is a specific type of T-rule used for handling syntactic structures

Examples of T-rules

  • PLR:=0>"s"; (A-rule: add "s" in case of plural, as in book>books)
  • MTW:=+VA("into account",PP); (C-rule: add the prepositional phrase "into account" as an adjunct to the verbal phrase (VA) in order to form the multiword expression, as in take>take into account)
  • (ART,%x)(QUA,%y):=(%y)(%x); (L-rule: reverse the order ART+QUA to QUA+ART, as in the all>all the)
  • ("don't"):=("do not"); (N-rule: replace the contraction "don't" by "do not")
  • (V,%x)(N,%y):=VC(%x;%y); (S-rule: replace the linear relation between a verb and a noun by the syntactic relation VC between them)

D-rules

main article: D-rule

D-rules are used to control the action of T-rules. They are used to control the dictionary retrieval (in tokenization) and to prevent or to induce the application of rules in transformation.

D-rules follow the syntax:

α=P;

where the left side α is a statement and the right side P is an integer from 0 to 255 that indicates the probability of occurrence of α.

Examples of D-rules

  • (ART)(VER)=0; (there cannot be any article before a verb)
  • agt(^V,^J;)=0; (the source node of an agent relation must be either a verb or an adjective)
  • (D)(N)=1; (determiners may come before nouns)

Modules

In the UNL framework there are three types of grammar:

  • N-Grammar, or Normalization Grammar, is a set of T-rules used to segment the natural language text into sentences and to prepare the input for processing.
  • T-Grammar, or Transformation Grammar, is a set of T-rules used to transform natural language into UNL or UNL into natural language.
  • D-Grammar, or Disambiguation Grammar, is a set of D-rules used to to improve the performance of transformation rules by constraining or forcing their applicability.

Direction

In the UNL framework, grammars are not bidirectional, although they share the same syntax:

  • UNLization (NL>UNL)
    • The N-Grammar contains the normalization rules for natural natural analysis
    • The Analysis T-Grammar contains the transformation rules used for natural language analysis
    • The Analysis D-Grammar contains the disambiguation rules used for tokenization and for improving the results of the NL-UNL T-Grammar
  • NLization (UNL>NL)
    • The Generation T-Grammar contains the transformation rules used for natural language generation
    • The Generation D-Grammar contains the disambiguation rules used for improving the results of the UNL-NL T-Grammar

Processing Units

In the UNL framework, grammars may target different processing units:

  • Text-driven grammars process the source document as a single unit (i.e., without any internal subdivision)
  • Sentence-driven grammars process each sentence or graph separately
  • Word-driven grammars process words in isolation

Text-driven grammars are normally used in summarization and simplification, when the rhetorical structure of the source document is important. Sentence-driven grammars are used mostly in translation, when the source document can be treated as a list of non-semantically related units, to be processed one at a time. Word-driven grammars are used in information retrieval and opinion mining, when each word or node can be treated in isolation.

Recall

Grammars may target the whole source document or only parts of it (e.g. main clauses):

  • Chunk grammars target only a part of the source document
  • Full grammars target the whole source document

Precision

Grammars may target the deep or the surface structure of the source document:

  • Deep grammars focus on the deep dependency relations of the source document and normally have three levels (network, tree and list)
  • Shallow grammars focus only on the surface dependency relations of the source document and normally have only two levels (network and list)

Assessment

Main article: F-measure

Grammars are evaluated through a weighted average of precision and recall, the F-measure.

Software