the verbal phrase of northern sotho: a morpho-syntactic perspective

The verbal phrase of Northern Sotho:A morpho-syntactic perspective

Gertrud Faaß

Universitat StuttgartInstitut fur maschinelle Sprachverarbeitung

– Computerlinguistik –Azenbergstr. 12

D 70174 Stuttgart

2nd AfLaT-Workshop (LREC 2010)May 18th, 2010

Faaß (IMS) Parsing Northern Sotho VPs May 18th, 2010 1 / 26

This Talk

Methodology

Language introduction(alongside two example sentences)

Some word classes(parts of speech)

The verbal phrase (VP): Basic layout / moods

Parsing Northern Sotho VPs


Methodological approach

1 Study linguistic descriptions of the language, enhance, if necessary:Move from a linguistic language-specific approach to a more generaltheoretical approach with a focus on implementability

2 Apply new knowledge to known theories, enhance, if necessary:Northern Sotho: do not differ between morphological and syntacticprocesses → morpho-syntactic representations

3 Implementation

– Preparation: Describe constellations based on type of the language:Sotho is a configurational language with a rather fixed word order→ define possible XPs on token/POS level

– Implementation of some constellations using PARC’s “xle” (LFG)

4 Evaluation (student’s work): e.g. development of an NP chunker


Language IntroductionSotho vs. Nguni vs. otherssource: David Joffe’s African Languages page: http://africanlanguages.com/


http://africanlanguages.com/

Two example sentences

[S ‘a man buys books’ ]monna o reka dipukunoun subject concord verb nounof class 1 of class 1 stem of class 10(the) man subj-3rd-01 [to] buy (the) books[N01 ] [1CS01 ] [Vtr ] [ N10][NP01 ] [VP01 ]

[S ‘they help him/her’ ]ba a mo thusasubject concord morpheme object concord verb stemof class 2 present of class 1(Subj-V-agreement) tensesubj-3rd-02 pres obj-3rd-01 [to] help[1CS02 ] [MORPHpres] [C001 ] [Vtr ][VP ]


NominalsBantu Languages in general make use of a noun class system

Properties of nominal items:

Lack of determiners (NP → N)

Bantu languages in general: up to 24 noun classes ([Mutaka(2000), p. 151])

(no number/gender, all 3rd person),Northern Sotho makes use of

– classes 1 - 10, 14– class 15 = infinitive (verbal properties - separate issue)– classes 16 - 18, nasal- an ga- are all locative classes

([Taljard et al.(2008)Taljard, Faaß, Heid, and Prinsloo] summarise them as “loc”)

monna o reka dipukuba a mo thusa


Nominals (cont.)Morpho-syntactic properties

Nouns may be omitted whenever they are known in the discourse

Any element agreeing with it is then acquiringits grammatical function:bannaSUBJ ba a mo thusa ((the) men help him/her)baSUBJ a mo thusa (they help him/her


Nouns: Nclass

Table: Words formed with the root -dimo

class noun translation1 Modimo God (common noun?)1 modimo ghost, spirit of a deceased2 badimo ghosts/spirits of the deceased3 modimo evil spirit4 medimo evil spirits5 ledimo thunderstorm6 madimo thunderstorms7 sedimo sacrifice8 didimo sacrifices14 bodimo cannibalism

LOC godimo high above, in the air

[Heid et al.(2009)Heid, D.J., Faaß, and Taljard] describe the design of a noun guesser for POS-tagging (accuracy 92%)


The verb stem and its arguments: Vtransitivity

intransitivesepela → [to] walktransitive: V + ARGthusa monna → [to] help (a/the) mantransitive: CO + Vmo thusa → [to] help him/hertransitive: CO + V (fused form)nthusa → [to] help medouble transitive: V + ARG1 + ARG2direla monna kofi → [to] make coffee for the mandouble transitive: CO + V + ARG1mo direla kofi → [to] make coffee for him/her

Future: Research on verbal subcategorization frames of Northern Sothomonna o reka dipukuba a mo thusa


Verbal suffix (clusters) and verbal endingsChanging argument structure / tense:base [to] mod. rule resultdira make applic. -el- direla [to] make X for Ybona see pass. -w- bonwa [to] be seenre say past -il-+-e itse saiddirela make+appl. past -el- diretse made X for Yngwala write * ngwadisitswego **

* = verb + causative (-is-) + perfect (-il-) + passive (-w -) +(-e-) + relative marker (-go)** = who are registered/enrolled

Verbal ending (Vend) depends on mood / polarity / fused form / object concord:

base [to] mod. rule resultsepela walk imp. +-a,-ang sepela! (yousg) walk!

sepelang! (youpl) walk!le bula close it imp. +-e,-eng le bule! (yousg) close itcl05!

+-e,-eng se sepele! (yousg do not) walk!se sepeleng! (youpl do not) walk!

[Prinsloo et al.(2008)Prinsloo, Faaß, Taljard, and Heid] developed a verb guesser achieving 94% recall, 88% precisionFaaß (IMS) Parsing Northern Sotho VPs May 18th, 2010 10 / 26

Object concords: COclass/pers(1st/2nd)

Object concords are the only “pronouns” in the traditional sense ofthe word: replacing an omitted (or topicalised) noun/NP

Double transitive verbs: Only one of its objects may bepronominalised (usually the indirect one)

Always precede the verb stem directly (may be fused, cf. nthusa)

classPERS 1sg ... PERS 2pl 01 02 03 04 05 ... LOC

N- le mo ba o e le go

ba a mo thusa


Subject concords: setCSclass/pers(1st/2nd)

Different moods → Different sets of subject concords

classset PERS 1sg PERS 2sg .. 1 2 3 4 5 61 ke o .. o ba o e le a2 ke o .. a ba o e le a3 ka wa .. a ba wa ya la a

indicative: monna o reka dipuku ((a) man buys books)

situative: ge monna a reka dipuku (when (a) man buys books)


Concordial items

‘‘...strictly speaking, any linguistic element which agreeswith a noun can acquire a pronominal function

when that noun is deleted...’’ [Louwrens(1991), p. 154]

→ Northern Sotho is a “null-subject” language

Concordial elements may be highly ambiguous([Faaß et al.(2009)Faaß, Heid, Taljard, and Prinsloo])

e.g. o:

– subject concord of classes 1/3, and 2nd pers. sg– copulative verb for classes 1/3 and 2nd pers. sg.:

(subject concords may appear as copulative verbs)– object concord of class 3

o reka dipuku → (s)he (class 1) / (s)he/it (class 3) / you (2nd pers. sg) buy bookso morutisi → (s)he is / yousg are a teacher

ba a mo thusa → they (class 2) pres him/her (class 1) help


Tense morphemes: MORPHtense

Table: Tense/Aspect morphemes

Morpheme Indication Comments

a pres. only appears in the positiveindicative mood(if verb ends in verb stem)

tlo/tla future tlo and tla appear interchangeablya past only appears in the negative

perfect indicative mood

ka potential used in the sense of “may possibly”

pres ba a mo thusa They help him/herfuture ba tlo mo thusa They will/shall help him/her

potential ba ka mo thusa They might help him/her


Negation morpheme (clusters): MORPH neg

Table: Negated indicative mood: constellations

pres. <ga> 2CScateg verb(+ -e)(+object(s))past 1 <ga se> 3CScateg verb(+ -a)(+object(s))past 2 <ga se> 2CScateg verb(+ -e)(+object(s))past 3 <ga> 3CScateg verb(+ -a)(+object(s))past 4 <ga> a 1CScateg verb(+ -a)(+object(s))fut 2CScateg<ka se> verb(+ -e)(+object(s))

pres ga ba mo thuse They do not help him/her

future/potential ba ka se mo thuse They will/shall not help him/her


Northern Sotho indicative: pres + futindicative

indicative pres pos monna o1CS01 reka dipukumanN01 subj-3rd-01 buy books

ba1CS01 a mo thusasubj-3rd-01 pres obj-3rd-01 help

indicative pres neg monna ga a2CS01 reke dipukumanN01 neg subj-3rd-01 buy books

ga ba1CS01 mo thuseneg subj-3rd-01 obj-3rd-01 help

indicative fut pos monna o1CS01 tlo reka dipukumanN01 subj-3rd-01 fut buy books

ba1CS01 tlo mo thusasubj-3rd-01 fut obj-3rd-01 help

indicative fut neg monna a2CS01 ka se reka dipukumanN01 subj-3rd-01 pot neg buy books

ba2CS02 ka se mo thusesubj-3rd-01 pot neg obj-3rd-01 help


VP examinationAnalysis of the data

General rules for morpho-syntactics of the Northern Sotho verb– The verb’s arguments always follow the verb stem– One of them may be pronominalised;

the object concord precedes the verb stem– All other elements appear in front of verb and object(s)

Verb stem an its objects appear independently from other elements– Negation (clusters), potential morpheme and subject concord

appear as a group– Only one tense morpheme may appear after these

The appearances of other elements influence– mood (incl. polarity/tense/aspect)– agreement with the subject

These elements appear independently from verb stem and its objects→ Attention:

“Interaction” between the ending of the verb stem and themood/polarity


VP: layoutThe Verbal Phrase: VBP+VIE

Idea: Split the linguistic verb into two parts:

1 The verb stem and its arguments(constellations are dependent on the verbal semantics/the discourse)

2 All other morphemes/concords (constellations define the mood)

Definitions:

Slot system:1 Verb and objects = Verbal Basic Phrase (VBP) = slot “zero”

(VP in the case of the positive imperative mood)

Add two preceding “slots”:

– slot “zero-1” optional, contains at max. one tense morpheme– slot “zero-2” optional, contains subject concord and negation/potential

morpheme (clusters)

2 slots “zero-1” and “zero-2”: Verbal Inflectional Element


VP definitionindicative

VIE VBP

zero-2 zero-1 zero

CS/MORPH neg/MORPH pot MORPH tense CO V OBJ-NPs

indicative pres pos monna o1CS01 reka dipukumanN01 subj-3rd-01 buy books

ba1CS01 a mo thusasubj-3rd-01 pres obj-3rd-01 help

indicative pres neg monna ga a2CS01 reke dipukumanN01 neg subj-3rd-01 buy books

ga ba1CS01 mo thuseneg subj-3rd-01 obj-3rd-01 help

indicative fut pos monna o1CS01 tlo reka dipukumanN01 subj-3rd-01 fut buy books

ba1CS01 tlo mo thusasubj-3rd-01 fut obj-3rd-01 help

indicative fut neg monna a2CS01 ka se reka dipukumanN01 subj-3rd-01 pot neg buy books

ba2CS02 ka se mo thusesubj-3rd-01 pot neg obj-3rd-01 help


VP rules(VIE +) VBP= VP

Slots for VBP:VBP

pos-1 pos0 pos+1 pos+2

CO V ARG-1 ARG-2

The rules describing the VBP slots depend on

number/kind of arguments of the verb stem (semantics)

whether one of the (nominal) arguments is replaced by an object concord

Rules describing VPs (excerpt):VIE VBP

indicative pres pos 1CScateg VBPindicative pres neg ga 2CScateg VBPindicative fut pos 1CScateg MORPH fut VBPindicative fut neg 2CScateg ka se VBPsituative pres pos 2CScateg VBPsituative pres neg 2CScateg sa VBP...relative perf. neg1 2CScateg sego/seng 3CScateg VBP...imperative pos – VBP


A toy grammar of Northern SothoParametrisation of V-Stem ending and VIE elements

Parametrisation of V-Stem ending: “Vend”caters for allomorphy / irregular forms / mood assignment→ put into lexicon

–re Vend = “a” ([to] say)bontshitse Vend = “ile” (showed)dutse Vend = “a” ([to] sit, dula (go to sit)

Parameters may be used by grammar rules as constraints(e.g. if present tense, positive, indicative mood, then lexicon entryof V must contain a parameter Vend that must have a assigned)

Parametrisation of all elements of the VIE “MOOD”, “clause type”

– Subject concord (noun class for subject-verb agreement) “class”– Tense / Aspect morphemes (tense, modal information) “TENSE”– Negation (positive/negative): “pol(arity)”)


A toy grammar of Northern SothoImplementation Lexical Functional Grammar (LFG) (courtesy: Pablo Alto Research Center)

lexicon: small

rules: so far, only imperative + indicative + infinitive implemented

still loads to do!

PARallel GRAMmar project: Northern Sotho LFG will be on the web!


Implementation: A toy grammar of Northern SothoAnalyses of Ba thusa banna. / Ba a mo thusa. / Nthuse! / Monna o reka dipuku.

Constituent-Structures


Implementation: A toy grammar of Northern SothoAnalyses of Ba thusa banna. / Ba a mo thusa. / Nthuse! / Monna o reka dipuku.

Functional-Structures


Acknowledgements

This work is describing core parts of my PhD thesis - THANKS to

My supervisors:Prof. Daan J. Prinsloo University of Pretoria, South Africa

PD Dr. phil. habil. Ulrich Heid, apl. Prof. Universitat Stuttgart, Germany

The staff at the department of African Languages, Uni Pretoria,especially Prof. E. Taljard

The DAAD for the scholarship, the NRF for the infrastructure

...


References

G. Faaß, U. Heid, E. Taljard, and D.J. Prinsloo.

Part-of-Speech tagging in Northern Sotho: disambiguating polysemous function words.In Proceedings of the EACL2009 Workshop on Language Technologies for African Languages – AfLaT 2009, pages38 – 45. The 12th Conference of the European Chapter of the Association for Computational Linguistics, 30th March to3rd April 2009.

U. Heid, Prinsloo D.J., G. Faaß, and E. Taljard.

Designing a noun guesser for part of speech tagging in Northern Sotho.South African Journal of African Languages (SAJAL), 29(1):1 – 19, 2009.

L.J. Louwrens.

Aspects of the Northern Sotho Grammar.Via Afrika, Pretoria, South Africa, 1991.

N.N. Mutaka.

An Introduction to African Linguistics.LINCOM Handbooks in Linguistics 16. LINCOM EUROPA, Munchen, 2000.

D.J. Prinsloo, G. Faaß, E. Taljard, and U. Heid.

Designing a verb guesser for part of speech tagging in Northern Sotho.South African Linguistics and Applied Language Studies (SALALS), 26(2):185 – 196, 2008.

E. Taljard, G. Faaß, U. Heid, and D.J. Prinsloo.

On the development of a tagset for Northern Sotho with special reference to the issue of standardization.Literator – special edition on Human Language Technologies, 29(1):111 – 137, 2008.


the verbal phrase of northern sotho: a morpho-syntactic perspective

Technology

mo thusafaa ims

comfaa ims

himherfaa ims

precisionfaa ims

stem of class

mo ba o e

np chunkerfaa ims

present of class