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Metagrammars as Logic Programs
Denys Duchier, Yannick Parmentier, Simon Petitjean
To cite this version:
Denys Duchier, Yannick Parmentier, Simon Petitjean. Metagrammars as Logic Programs. 7th Inter-
national Conference on Logical Aspects of Computational Linguistics (LACL 2012, demo session), Jul
2012, Nantes, France. pp.1-4. �hal-00696562�
DenysDuhier,YannikParmentier,andSimonPetitjean
LIFO,Universitéd'Orléans, Bâtiment3IA
6,RueLéonardDeVini-BP6759
F-45067OrléansCedex2,Frane,
firstname.lastnameuniv-orlea ns.fr
Abstrat. In this paper, we introdue the eXtensible MetaGrammar
(XMG), whih orresponds to both a language for speifying formal
grammars,andaompiler for thislanguage.XMGhas beendeveloped
overthelast deadeto providelinguistswith adelarativeand yetex-
pressive way tospeifygrammars.Ithas beenappliedto thedesignof
atualtree-basedgrammarsforFrenh,GermanorEnglish.XMGrelies
onamodulararhiteture,whihmakesitpossibletoextendtheformal-
ismwithadditional levelsofdesriptions and/or linguistiproperties.
Thus,ontopofsyntax,XMGanalsobeusedforthedesriptionofother
linguistiinformationsuhassemantis,ormorphology(thelatterbeing
urrentlyexploredforIkota,anAfrian languagespokeninGabon).
1 Introdution
SineChomsky'sseminalworkongenerativegrammar[1℄,manyformalsystems
have been proposed to desribe the syntax of natural language (see e.g. [2℄).
Thesemainly dierintermsofexpressivityandomputationalomplexity,and
generally rely either on rewriting rules (e.g. Tree-Adjoining Grammar), or on
onstraints(e.g. Head-drivenPhrase StrutureGrammar).
1
Aninterestingfamilyofformalgrammarsarelexializedgrammars[3℄.Suh
grammarsassoiateeahelementarystruture(i.e.grammarrule)withalexial
item (alled anhor).Lexialized grammars oertwo main advantages:rstly,
the grammar an be seen as a funtion mapping lexial items (i.e. words)
withuninstantiatedgrammatialstrutures(thegrammaristhenalledlexion).
Seondly,asubgrammaranbeextratedfromtheinputgrammaraordingto
thesenteneto parse,thusspeedingupparsing.
Anexampleof lexializedgrammaris LexializedTree-AdjoiningGrammar
(LTAG). In this formalism, the grammar is made of (thousandsof) uninstan-
tiated elementary trees(alledtree templates),where theleafnodesontainat
leastoneanhornode(labelledwith⋄).Theseanhornodesareattahedtoad-
equatelexialitemsatparsing.Asanillustration,onsiderFig.1depitingtwo
treetemplatestobeanhoredwithatransitiveverbsuhas manger(toeat).
1
We donotdisussthedistintionbetween onstituenyanddependenygrammar
S
N↓ V⋄ N↓
Jean mange unepomme
John eats anapple
N⋆ S
C
que
S
N↓ V⋄
La pommeque Jean mange
The applethat John eats
Fig.1.ElementarystruturesofanLTAG
From alinguistipointof view,lexialized grammarsallow to express gen-
eralizationsoverlexialentries bygatheringtreetemplates,whose anhorhave
similar syntati properties, into tree families. From a omputational point of
view, lexialized grammars are made of a huge number of strutures, due to
redundanywithin thelexion (e.g.treetemplatessharingommonsubtrees).
TheoneptofmetagrammarwasintroduedbyCandito[4℄inordertodeal
withstruturalredundanybyapturinggeneralizationsovertreetemplates.In-
stead of diretly desribingthe syntax of languagevia aformal grammar,the
linguistspeiesthestruturesofthisformalgrammarusingadediatedframe-
work.Thisspeiationofthegrammarisalledametagrammarandisautomat-
iallyproessed to generatethe grammar.Manymetagrammatialframeworks
havebeenproposed forLTAG[4,5,6,7℄.Here weintrodueone ofthese,namely
eXtensibleMetaGrammar(XMG)[6℄.XMGdiersfromothermetagrammarap-
proahesbyitsdelarativespeiationlanguage,anditsmodulararhiteture.
The latter made it possible to extend the onept of metagrammars to other
levelsofdesription(e.g. morphology)andlinguistipriniples(e.g. onstraints
onwordorder),asweshallseebelow.
2 The XMG language
As mentionedabove, the XMG languageallows for a delarative speiation
oflinguististrutures(inludingtreedesriptions).Morepreisely,XMGoers
a uniation-based language à la Prolog to speify what a grammar is. This
speiation is then proessed by the XMG ompiler in order to produe a
omputationalgrammar(e.g. anLTAG),whihan besavedin anXML le.
Capturingredundanyusingabstrations.XMGreliesontheoneptofabstra-
tiontoallowthelinguist torefertoreusablegrammatialunits (e.g. (ombina-
tionsof)treefragmentsforLTAG).Formally,anXMGspeiationorresponds
todelarativerules,whihanbedenedusingthefollowingabstratsyntax:
Rule := Name→Content
Content := Contribution | Name | Content∨Content | Content∧Content
Here,Contributionreferstoalinguistifragmentofinformationofagiventype
sriptionlanguagewhendesribingsyntaxwithLTAG).Thislanguagerelieson
uniationvariablestoshareinformationbetweendistintXMGrules(i.e. dis-
tintgrammatialunits) orbetweendistintontributions(i.e.betweensyntax
andsemantis).Thesopeofthesevariablesisbydefaultrestritedtotherule,
butanbeextendedviaimport/exportdelarations.Asatoyexampleofthese
variables and of XMG onrete syntax, onsider the rules CanonialSubjet
and Subjet below, the latter speies a generalization overthe two possible
realizationsofasubjetshowninFig.1(->isdominaneand>>preedene).
lassCanonialSubjet %% (omment)alass isan XMGrule in theabstratsyntax
export ?x ?y
delare ?x?y ?z ?u
{<syn> %% ontributionoftype <syn>
{node ?x [at=S℄;node ?z [at=N℄;node ?y (type=anhor)[at=V℄;node?u [at=N℄;
?x -> ?z;?x -> ?y ;?x-> ?u ;?z>> ?y ;?y>> ?u }
}
lassSubjet {CanonialSubjet[℄ |RelSubjet[℄}
Towardsuser-deneddesriptionlanguages.Metagrammarsbringinterestingin-
sightsin grammarengineering byoeringan abstrat viewonlanguage,made
ofombinationsofgrammatialunits.Sofar,theseunitsweredesribedusinga
set of hard-oded desriptionslanguages.Toreah extensibility, weare explor-
ing another approah: permittinguser-dened desription languages(similarly
tothegrammar,thesemustbedesribed).Somepartsoftheompilerthushave
tobegeneratedautomatially.
3 The XMG ompiler
General arhiteture. As mentioned above, the XMG language is nothing else
thanalogilanguage.Itsompilerthussharesomefeatureswithaompilerfor
logi programs. First, the lasses omposing the metagrammar (dened using
theXMGlanguageintroduedabove)areonvertedintolausesofanExtended
Denite Clause Grammar (EDCG) [8℄, whih orresponds to a DCG having
multiple aumulators. This underlying EDCG expliits the aumulation of
ontributions of multiple types (e.g. syntax, semantis). Then, this EDCG is
evaluatedaordingtoaxiomsdenedinthemetagrammar(omparabletoPro-
log queries). This produes alist of tuples of ontributions (the arity of these
tuples is the number of ontribution types). Finally, eah tuple of this list is
optionally post-proessed. For instane, tuples whose syntati ontribution is
atree desription arefed to asolverin order to produe syntatitrees. Dur-
ingthissolvingstep,itispossibletoapplylinguistiwell-formednesspriniples
(thesean useinformationfrom otherontributionsofthetuple).
XMG 2. The rst version of XMG (XMG 1.x) was developed between 2003
and 2010 in the Oz programming language, and inluded only three desrip-
tionlanguages:oneforspeifyingsyntatitrees(eitherLTAGtreetemplatesor
InterationGrammartreedesriptions),oneforspeifyingsemantirepresenta-
der to extendXMGwith theabilityto dene an arbitrarynumberof typesof
ontributions(andthusofuser-deneddesriptionlanguages).
2
4 Current state and future work
XMGan beused todesribetreestrutures, featurestrutures, prediates,or
propertiesofthePropertyGrammarformalism.Version2oftheXMGlanguage
superseedsVersion1(beingbakward-ompatible).XMG2anbeusedtoom-
pile grammars designed with XMG1, inluding theFrenh LTAG and Frenh
Interation Grammar,whose XMG metagrammarsareavailable on-line(along
withtoyexamplesofXMGinput/output).
3
WhendesribingLTAGtreetem-
plates,XMG2oersspeilinguistipriniples,namelyorderingbetweensister
nodes,uniqueness ofagivennodelabel,and nodemergingviapolarities.
XMG 2 is being atively developed in order to allow for ross-framework
grammarengineering, inthelinesof [9℄,but alsoforlinguistiexperimentation
bydeningdynamiallyitsowngrammarformalismasmentionedinSetion2.
XMG2hasbeenusedreentlytodesribethemorphologyofverbsinIkota,
an agglutinative Bantu language spoken in Gabon [10℄. The idea behind this
workistospeifymorphemesasontributionsintermsoflexialphonologyand
inetion (morpho-syntati features). In a next step, we plan to extend this
metagrammar(i.e. thisabstratlinguistiaountofmorphology)tosyntax.
Referenes
1. Chomsky,N.: SyntatiStrutures. Mouton,TheHague(1957)
2. Abeillé,A.: LesNouvellesSyntaxes. ArmandColin,Paris(1993)
3. Shabes,Y., Abeillé, A., Joshi,A.K.: Parsing strategieswith 'lexialized' gram-
mars:appliationtoTreeAdjoiningGrammars.In:12thCOLING.(1988)578583
4. Candito, M.: APriniple-Based Hierarhial Representation ofLTAGs. In:16th
COLING.(1996)194199
5. Xia, F.: AutomatiGrammarGenerationfrom two Dierent Perspetives. PhD
thesis,UniversityofPennsylvania(2001)
6. Duhier,D.,LeRoux,J.,Parmentier, Y.: TheMetagrammarCompiler:AnNLP
AppliationwithaMulti-paradigmArhiteture. In:MOZ.(2004)175187
7. VillemonteDeLa Clergerie, É.: Building fatorized TAGswithmeta-grammars.
In:TAG+10,NewHaven,CO,UnitedStates(2010)111118
8. VanRoy,P.:Extendeddgnotation:Atoolforappliativeprogramminginprolog.
Tehnialreport,TehnialReportUCB/CSD90/583,UCBerkeley(1990)
9. Duhier,D.,Parmentier,Y.,Petitjean,S.:Cross-frameworkGrammarEngineering
using Constraint-drivenMetagrammars. In:CSLP.(2011)3243
10. Duhier, D., Magnana Ekoukou, B., Parmentier, Y., Petitjean, S., Shang, E.:
DesribingMorphologially-rihLanguagesusingMetagrammars:aLookatVerbs
inIkota. In:4thWorkshoponAfrianLanguageTehnology-LREC.(2012)
2
Bothimplementations(XMG1.xandXMG2.x)arefreelyavailableon-lineathttps:
//souresup.renater.fr/xmgandhttps://launhpad.net/xmg respetively.
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