Building a Dictionary of Affixal Negations

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Chantal van Son, Emiel van Miltenburg, Roser Morante (VU Amsterdam)c.m.van.son@vu.nl

ExProM Workshop @ COLING 2016Special Session on Negation

December 12, 2016 - Osaka, Japan

Introduction: Affixal negations

• Words marked with negative affix; typically flag the absence of particular features

• English: un-, in-, dis-, a-, an-, non-, im-, il-, ir-, -lesse.g. unable, disagree, impossible

• Automatic detection could benefit NLP tasks such as text mining, recognizing textual entailment, paraphrasing and QA

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Introduction: Affixal negations

• Blanco & Moldovan (2011): very difficult to detect without substantial false positive rate • how to distinguish between ineffective and invite?

—> check whether word is still valid after removing prefix: how to prevent inform from being annotated?

• how do deal with ambiguity: invalid (a) vs. invalid (n)?

• Automatic detection might benefit from dictionary-based approach

3 Eduardo Blanco and Dan Moldovan. 2011. Some issues on detecting negation from text. In Proceedings of the24th International Florida Artificial Intelligence Research Society Conference , pages 228–233.

Overview of today’s talk

1. Defining lexical negation 1. affixal negations and regular antonyms 2. typology of affixal negations (Joshi 2012)

2. Building a negation dictionary (preliminary study) 1. annotation tasks 2. evaluation

3. Discussion & Conclusion

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Defining lexical negation

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Affixal negation

• Morante and Daelemans (2012): annotation of (affixal) negation in two Conan Doyle stories

• Main goal: to annotate information relative to the negative polarity of an event (negation + scope)

• ‘Narrow’ definition: only annotated if they are direct antonyms of their non-affixed base • unclear (not clear) • disappear (*not appear), unspoken (*not spoken)

• What is considered an affixal negation should depend on the task at hand

6 Roser Morante and Walter Daelemans. 2012. Conan Doyleneg: Annotation of negation in Conan Doyle stories.In Proceedings of the Eighth International Conference on Language Resources and Evaluation (LREC) .

Semantic categories (Joshi 2012)

• Joshi (2012): distinction between direct and indirect affixal negations

• Direct: direct opposition with its positive counterpart and characterized by the NOT-element (e.g. unhappy)

• Indirect: does not logically negate the existence of its base, yet still maintains a negative connotation (e.g. disconnect, debug)

7 Shrikant Joshi. 2012. Affixal negation – direct, indirect and their subtypes. Syntaxe et semantique, (1):49–63.

Semantic categories (Joshi 2012)

8 Shrikant Joshi. 2012. Affixal negation – direct, indirect and their subtypes. Syntaxe et semantique, (1):49–63.

Table: Subtypes of indirect negation from (Joshi, 2012, p. 27).

Relation to regular antonyms

• Full range of lexical opposites • The difference between affixal negations and

regular antonyms is only morphological

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a. distasteful (a ‘true’ affixal negation) b. disgusting (only etymologically an affixal negation) c. dead (a regular antonym)

continuous scale going from explicitly (a) to implicitly (c) marked

Full range of negation

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Figure: Taxonomy of negations, based on (Joshi, 2012)

Antonymy in WordNet

• Direct antonymy: a lexical relation between individual lexemes that have clear opposite meanings (wet:dry, clear:unclear)

• Indirect antonymy: results from similarity relations defined for the members of direct antonym pairs (moist:dry, legible:unclear)

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Antonymy in WordNet

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Figure: Similarity and antonymy relations in WordNet, from (Gross and Miller, 1990).

Building a negation dictionary

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Annotation of WordNet antonyms

• Ideal lexical negation dictionary: regular antonyms + affixal negations specified for their subtypes

• Starting point: all direct antonyms in WordNet (3,557 pairs, including verbs, nouns, adjectives and adverbs)

• We included the following information from WordNet:

• the lemmas of both antonyms • the lemma identifiers of both antonyms • the definitions of both antonyms • the part of speech

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Annotation tasks

• Two expert annotators

• Three annotation tasks

1. Affixal or non-affixal

2. Direct or indirect (if affixal)

3. Subtype: 9 subtypes by (Joshi 2012) + additional label LACKING (if indirect)

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Example of entries

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Table: Simplified examples of entries of affixal negations in the dictionary

Evaluation: IAA

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Subtask 1:Affixal or non-affixal

Subtask 2:Direct or indirect

Subtask 3:Subtype

n (antonym pairs) n = 500 n = 268 n = 43

Cohen’s kappa 0.80 0.55 0.76

Evaluation: confusion matrix

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Table: Confusion matrix for the annotation of subtypes

Evaluation: confusion

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Table: Antonym pairs where both annotators recognized an indirect affixal negation but disagreed on the subtype.

Discussion

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Discussion: doubt case (1)

fasten:unfasten Reversal of Action fastened:unfastened Direct negation

States expressed by participles (adjectives) with a negative affix can be interpreted as:

A. Indirect negation: a result of the action expressed by its verbal base (unfasten)

B. Direct negation: the opposite of another state, i.e. its antonym (fastened)

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Discussion: doubt case (2)

Another example: spinous:spineless

• Affix -less indicates indirect negation (lacking something) w.r.t. its base spine

• But: spineless is direct negation w.r.t. spinous

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Discussion

• Two options to consider for annotation:

A. relation between affixed form and its base (spine:spineless)

B. relation between two members of antonym pair (spinous:spineless)

• In case of (a): what exactly should be considered the base? E.g. unfastened: fastened vs. fasten

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Discussion

• A negation dictionary is only as good as its coverage

• Affixal negation is productive phenomenon; what could be a fallback strategy? —> training a classifier for detection and classification

• We still need to think about what relations this classifier should learn (annotation guidelines)

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Conclusion

• Set out the full scope of (lexical) negation

• Explored the possibility of an affixal negation/regular antonyms dictionary to support automatic detection

• Preliminary study: annotated WordNet’s direct antonym pairs

• No definite solution, but we hope it contributes its share to the discussion by highlighting some of the main issues to be considered

• The annotations are openly available at: https://github.com/cltl/lexical-negation-dictionary

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Thank you for your attention

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c.m.van.son@vu.nl

This work was supported by the Amsterdam Academic Alliance Data Science (AAA-DS) ProgramAward to the UvA and VU Universities, and by the Netherlands Organization for Scientific Research(NWO) via the Spinoza-prize awarded to Piek Vossen (SPI 30-673, 2014-2019).