Adapting NLP Tools and Frame-Semantic Resources for the Semantic - - PowerPoint PPT Presentation

▶
adapting nlp tools and frame semantic resources for the
SMART_READER_LITE
LIVE PREVIEW

Adapting NLP Tools and Frame-Semantic Resources for the Semantic - - PowerPoint PPT Presentation

Jun 22, 2023 283 likes •1.04k views

Adapting NLP Tools and Frame-Semantic Resources for the Semantic Analysis of Ritual Descriptions Nikolina Koleva UdS 22. February 2012 Nikolina Koleva (UdS) 22. February 2012 1 / 22 Outline Introduction 1 NLP Tools and Resources for

slide-1
SLIDE 1

Adapting NLP Tools and Frame-Semantic Resources for the Semantic Analysis of Ritual Descriptions Nikolina Koleva

UdS

  • 22. February 2012

Nikolina Koleva (UdS)

  • 22. February 2012

1 / 22

slide-2
SLIDE 2

Outline

1

Introduction

2

NLP Tools and Resources for Ritual Descriptions

3

Characteristics of Ritual Domain

4

Semantic Annotation of Ritual Descriptions

5

Detecting Ritual Structure

6

Summary

Nikolina Koleva (UdS)

  • 22. February 2012

2 / 22

slide-3
SLIDE 3

Motivation

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-4
SLIDE 4

Motivation

interdisciplinary subject, a bunch of challenges

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-5
SLIDE 5

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals?

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-6
SLIDE 6

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals? Does "ritual grammar" exist?

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-7
SLIDE 7

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals? Does "ritual grammar" exist? Is it universal?

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-8
SLIDE 8

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals? Does "ritual grammar" exist? Is it universal? There is evidence for variances and similarities in rituals wrt.

Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-9
SLIDE 9

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals? Does "ritual grammar" exist? Is it universal? There is evidence for variances and similarities in rituals wrt.

◮ culture Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-10
SLIDE 10

Motivation

interdisciplinary subject, a bunch of challenges Is there underlying structure of rituals? Does "ritual grammar" exist? Is it universal? There is evidence for variances and similarities in rituals wrt.

◮ culture ◮ time Nikolina Koleva (UdS)

  • 22. February 2012

3 / 22

slide-11
SLIDE 11

The Tasks

detection of complex event sequences

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-12
SLIDE 12

The Tasks

detection of complex event sequences finding participants, objects, places and times involved in the events

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-13
SLIDE 13

The Tasks

detection of complex event sequences finding participants, objects, places and times involved in the events How?

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-14
SLIDE 14

The Tasks

detection of complex event sequences finding participants, objects, places and times involved in the events How? → using NLP tools

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-15
SLIDE 15

The Tasks

detection of complex event sequences finding participants, objects, places and times involved in the events How? → using NLP tools recognition of variations and regularities of rituals

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-16
SLIDE 16

The Tasks

detection of complex event sequences finding participants, objects, places and times involved in the events How? → using NLP tools recognition of variations and regularities of rituals focus on discourse semantic aspects due to complex event sequences

Nikolina Koleva (UdS)

  • 22. February 2012

4 / 22

slide-17
SLIDE 17

Difficulties

no all-encompassing theoretical framework for ritual analysis thus recurrent structures in event sequences are unknown descriptions of rituals have different text features than texts used for the development of the used NLP tools → Need for adaptation

Nikolina Koleva (UdS)

  • 22. February 2012

5 / 22

slide-18
SLIDE 18

Resources and Tools for Analysis of Ritual Structure

Frame Semantics

◮ powerful framework: concept of scenario frames connected by frame

relations and role inheritance

Lexical Ontology, e.g. WordNet, for variation analysis in characteristics of events across rituals Semantically annotated corpora and reference ontology enables reasoning with external knowledge resources

Nikolina Koleva (UdS)

  • 22. February 2012

6 / 22

slide-19
SLIDE 19

Main steps

1 corpus creation and annotation ◮ contains descriptions of different cultures ◮ annotated with linguistic and ritual-specific tags 2 analysis of the ritual structure ◮ deployment of logical and statistical methods for the detection of

recurring structures and systematic variances in ritual descriptions based on semantic annotation

Nikolina Koleva (UdS)

  • 22. February 2012

7 / 22

slide-20
SLIDE 20

Ritual Descriptions

collected from different sources

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-21
SLIDE 21

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-22
SLIDE 22

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-23
SLIDE 23

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-24
SLIDE 24

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

◮ theory-oriented studies by ritual researchers that deal with religious,

ethnologic and social rituals (used to build ritual specific ontology)

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-25
SLIDE 25

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

◮ theory-oriented studies by ritual researchers that deal with religious,

ethnologic and social rituals (used to build ritual specific ontology)

◮ descriptions of rituals Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-26
SLIDE 26

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

◮ theory-oriented studies by ritual researchers that deal with religious,

ethnologic and social rituals (used to build ritual specific ontology)

◮ descriptions of rituals 1

ethnographic observations (How rituals are performed in modern times?)

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-27
SLIDE 27

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

◮ theory-oriented studies by ritual researchers that deal with religious,

ethnologic and social rituals (used to build ritual specific ontology)

◮ descriptions of rituals 1

ethnographic observations (How rituals are performed in modern times?)

2

ritual manuals (translations of original manuals that prescribe a ritual)

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-28
SLIDE 28

Ritual Descriptions

collected from different sources

◮ Hindu rituals from Nepal ◮ Middle East

textual sources

◮ theory-oriented studies by ritual researchers that deal with religious,

ethnologic and social rituals (used to build ritual specific ontology)

◮ descriptions of rituals 1

ethnographic observations (How rituals are performed in modern times?)

2

ritual manuals (translations of original manuals that prescribe a ritual)

◮ not trivial alignment of manuals that mention only relevant part of the

events to an exhaustive (possibly subjective description)

Nikolina Koleva (UdS)

  • 22. February 2012

8 / 22

slide-29
SLIDE 29

Text Characteristics

foreign terms

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-30
SLIDE 30

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa. Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-31
SLIDE 31

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-32
SLIDE 32

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-33
SLIDE 33

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh. Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-34
SLIDE 34

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh.

→replace with placeholders during processing and reinsert them afterwards

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-35
SLIDE 35

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh.

→replace with placeholders during processing and reinsert them afterwards

Imperatives, PPs and nested sentences

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-36
SLIDE 36

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh.

→replace with placeholders during processing and reinsert them afterwards

Imperatives, PPs and nested sentences

◮ very common and difficult to process Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-37
SLIDE 37

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh.

→replace with placeholders during processing and reinsert them afterwards

Imperatives, PPs and nested sentences

◮ very common and difficult to process

→ chunks are sufficient for semantic role labeling

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-38
SLIDE 38

Text Characteristics

foreign terms

◮ He sweeps the place for the sacrificial fire with kuśa.

→ He sweeps the place for the sacrificial fire with <grass *kuśa>.

fixed expressions that often have to be spoken

◮ Salutation to Kubera reciting the mantra arddha-mãsãh.

→replace with placeholders during processing and reinsert them afterwards

Imperatives, PPs and nested sentences

◮ very common and difficult to process

→ chunks are sufficient for semantic role labeling

comments occurence: not each sentence describes the ritual

Nikolina Koleva (UdS)

  • 22. February 2012

9 / 22

slide-39
SLIDE 39

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-40
SLIDE 40

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

◮ indicates event happening during the ritual performance: factual Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-41
SLIDE 41

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

◮ indicates event happening during the ritual performance: factual

The involvement of the nephews can be understood as a symbolic action to address those of the following generation who do not belong to lineage of the deceased.

Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-42
SLIDE 42

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

◮ indicates event happening during the ritual performance: factual

The involvement of the nephews can be understood as a symbolic action to address those of the following generation who do not belong to lineage of the deceased.

◮ another level of information, clear interpretation or comment:

interpretative /ignored for the frame annotation/

Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-43
SLIDE 43

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

◮ indicates event happening during the ritual performance: factual

The involvement of the nephews can be understood as a symbolic action to address those of the following generation who do not belong to lineage of the deceased.

◮ another level of information, clear interpretation or comment:

interpretative /ignored for the frame annotation/

The wife of the chief mourner [...] will carry a symbolic mat that represents the bed of the deceased[...].

Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-44
SLIDE 44

Sentence Classification

Salutation to Kubera reciting the mantra arddha-mãsãh.

◮ indicates event happening during the ritual performance: factual

The involvement of the nephews can be understood as a symbolic action to address those of the following generation who do not belong to lineage of the deceased.

◮ another level of information, clear interpretation or comment:

interpretative /ignored for the frame annotation/

The wife of the chief mourner [...] will carry a symbolic mat that represents the bed of the deceased[...].

◮ ambiguous wrt. these classes, or contain both Nikolina Koleva (UdS)

  • 22. February 2012

10 / 22

slide-45
SLIDE 45

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-46
SLIDE 46

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

◮ employ rule-based tokenizer that uses Unicode character ranges Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-47
SLIDE 47

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

◮ employ rule-based tokenizer that uses Unicode character ranges

poor results for PoS-Tagging and Chunking

Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-48
SLIDE 48

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

◮ employ rule-based tokenizer that uses Unicode character ranges

poor results for PoS-Tagging and Chunking

◮ a lot of unseen tokens Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-49
SLIDE 49

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

◮ employ rule-based tokenizer that uses Unicode character ranges

poor results for PoS-Tagging and Chunking

◮ a lot of unseen tokens ◮ many rare uncommon constructions Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-50
SLIDE 50

Linguistic Processing

many special non-English characters: ś, or even tokens: Gen .eśa

◮ employ rule-based tokenizer that uses Unicode character ranges

poor results for PoS-Tagging and Chunking

◮ a lot of unseen tokens ◮ many rare uncommon constructions

→ experiment with different scenarios for the domain adaptation

Nikolina Koleva (UdS)

  • 22. February 2012

11 / 22

slide-51
SLIDE 51

Experimental Design for Adaptation

two sources

Nikolina Koleva (UdS)

  • 22. February 2012

12 / 22

slide-52
SLIDE 52

Experimental Design for Adaptation

two sources

◮ 532 sentences of ritual descriptions, manually annotated with PoS and

Chunks

Nikolina Koleva (UdS)

  • 22. February 2012

12 / 22

slide-53
SLIDE 53

Experimental Design for Adaptation

two sources

◮ 532 sentences of ritual descriptions, manually annotated with PoS and

Chunks

◮ Wall Street Journal corpus Nikolina Koleva (UdS)

  • 22. February 2012

12 / 22

slide-54
SLIDE 54

Experimental Design for Adaptation

two sources

◮ 532 sentences of ritual descriptions, manually annotated with PoS and

Chunks

◮ Wall Street Journal corpus

10-fold cross-validation for evaluation

Nikolina Koleva (UdS)

  • 22. February 2012

12 / 22

slide-55
SLIDE 55

Evaluation of models for PoS-Tagging

Training data Accuracy (%) WSJ 90.90 RIT 94.82 WSJ + RIT 95.72 WSJ + RIT↑ 96.23 WSJ↓ + RIT 95.25 WSJ × RIT 96.86 WSJ × RIT ↑ 96.85 WSJ ↓ × RIT 95.92

Nikolina Koleva (UdS)

  • 22. February 2012

13 / 22

slide-56
SLIDE 56

Evaluation of models for Chunking

Training data F-measure(%) WSJ 86.6 RIT 85.7 WSJ + RIT 86.6 WSJ + RIT↑ 88.1 WSJ↓ + RIT 83.1 WSJ × RIT 74.4 WSJ × RIT ↑ 81.3 WSJ ↓ × RIT 73.3

Nikolina Koleva (UdS)

  • 22. February 2012

14 / 22

slide-57
SLIDE 57

Anaphora and Coreference Resolution

  • 1. The father should touch the girl [...]. Let him give a golden

coin as ritual fee[...].

  • 2. Let the girl sit on the seat [...]. Let the girl wash her face [...].

Nikolina Koleva (UdS)

  • 22. February 2012

15 / 22

slide-58
SLIDE 58

Anaphora and Coreference Resolution

  • 1. The father should touch the girl [...]. Let him give a golden

coin as ritual fee[...].

  • 2. Let the girl sit on the seat [...]. Let the girl wash her face [...].

BART /machine learning toolkit/; output entire coreference chain JavaRAP /rule-based/; generate only anaphor-antecedent pairs

Nikolina Koleva (UdS)

  • 22. February 2012

15 / 22

slide-59
SLIDE 59

Evaluation of Anaphora and Coreference Resolution

26 anaphor-antecedent pairs that correspond to 10 coreference chains

Nikolina Koleva (UdS)

  • 22. February 2012

16 / 22

slide-60
SLIDE 60

Evaluation of Anaphora and Coreference Resolution

26 anaphor-antecedent pairs that correspond to 10 coreference chains JavaRAP: 61.5% correct pairs found; evaluation only for anaphora resolution

Nikolina Koleva (UdS)

  • 22. February 2012

16 / 22

slide-61
SLIDE 61

Evaluation of Anaphora and Coreference Resolution

26 anaphor-antecedent pairs that correspond to 10 coreference chains JavaRAP: 61.5% correct pairs found; evaluation only for anaphora resolution

Nikolina Koleva (UdS)

  • 22. February 2012

16 / 22

slide-62
SLIDE 62

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-63
SLIDE 63

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-64
SLIDE 64

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-65
SLIDE 65

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

◮ some of them are equivalent only at a lexical level, occur in different

senses

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-66
SLIDE 66

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

◮ some of them are equivalent only at a lexical level, occur in different

senses

frames of FrameNet are too abstract for annotation of ritual descriptions

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-67
SLIDE 67

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

◮ some of them are equivalent only at a lexical level, occur in different

senses

frames of FrameNet are too abstract for annotation of ritual descriptions → new frames have to be designed

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-68
SLIDE 68

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

◮ some of them are equivalent only at a lexical level, occur in different

senses

frames of FrameNet are too abstract for annotation of ritual descriptions → new frames have to be designed train a frame-semantic labeler on initial frame inventory and annotated corpus (manually created)

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-69
SLIDE 69

Semantic Annotation of Ritual Descriptions

automatic extraction of verbs map the ritual actions to frames in FrameNet 80% of the verbs from the ritual corpus are contained as lexical units

◮ some of them are equivalent only at a lexical level, occur in different

senses

frames of FrameNet are too abstract for annotation of ritual descriptions → new frames have to be designed train a frame-semantic labeler on initial frame inventory and annotated corpus (manually created) manual correction after the automatic assignment of semantic roles

Nikolina Koleva (UdS)

  • 22. February 2012

17 / 22

slide-70
SLIDE 70

Detecting Ritual Structure |

  • 1. "... the boy sits downChange_posture south of the teacher. (The

teacher) takesTaking flowers, sandal, Areca nut and clothes and declaresText_creation the ritual decision to selectChoosing the Brahmin by sayingText_creation the mantra ..."

  • 2. "... (the teacher) placesPlacing (fire in a vessel of bell metal) in

front of himself. Having takenTaking flowers, sandal, Areca nut, clothing etc. he should selectChoosing a Brahmin. The Brahmin is selected withText_creation" the mantra ..."

Nikolina Koleva (UdS)

  • 22. February 2012

18 / 22

slide-71
SLIDE 71

Detecting Ritual Structure ||

interpret each frame and its roles as atomic symbol find global alignment between n sequences describing the same ritual

Nikolina Koleva (UdS)

  • 22. February 2012

19 / 22

slide-72
SLIDE 72

Summary

collecting texts: manuals and descriptions analysis of the domain characteristics adaptation of preprocessing tools and semantic resources detection of ritual structure and possible subsequences

Nikolina Koleva (UdS)

  • 22. February 2012

20 / 22

slide-73
SLIDE 73

Literature

[1] Nils Reiter, Oliver Hellwig, Anette Frank, Irina Gossmann, Borayin Maitreya Larios, Julio Rodrigues, and Britta Zeller. "Adapting NLP Tools and Frame-Semantic Resources for the Semantic Analysis of Ritual Descriptions". In: C. Sporleder, A. van den Bosch, and K. Zervanou (Eds.), Language Technology for Cultural Heritage. Selected Papers from the LaTeCH Workshop Series, Series: Theory and Applications of Natural Language Processing. Heidelberg: Springer, 2011. [2] Nils Reiter, Oliver Hellwig, Anand Mishra, Anette Frank, Irina Gossmann, Borayin Maitreya Larios, Julio Rodrigues, and Britta Zeller. "Adapting Standard NLP Tools and Resources to the Processing of Ritual Descriptions". Proceedings of ECAI 2010 workshop on Language Technology for Cultural Heritage, Social Sciences, and Humanities.

Nikolina Koleva (UdS)

  • 22. February 2012

21 / 22

slide-74
SLIDE 74

Thank you for your attention!

Nikolina Koleva (UdS)

  • 22. February 2012

22 / 22