Language-Independent Discriminative Parsing of

Temporal Expressions

CS 671 : Natural Language Processing

- Gabor Angeli, Jakob Uszkoreit

Introduction

• Probabilistic approach for extracting temporal information using latent parsing has been proposed.

• Temporal resolution is the process of relating a complex textual phrase with potentially complex time, date, or duration to an understandable normalized temporal representation.

• The proposed approach is multilingual.

Parsing Time

• Detection : Finding temporal phrases in a sentence.

• Interpretation : Finding the grounded meaning of the phrase

• Incorporate a reference time

Examples

Actually I am out of station in the last two weeks of September.

I have some time available at the end of next week.

They expect earnings to rise next month.

Hurry up, May 9 is next week, there's still a few days.

9-5 WXX ~1D[5-5-2013]

Reference Time [9-5-2013] [12-5-2013 / 18-5-2013] ~1D

Grammar of Time

• Range - A period between two dates• Sequence - A sequence of Ranges

Ex: Today is 2012-06-05 , what is last Sunday?

• Duration -A period of time: day, 2 weeks,2 years• Functions - General sequence and interval operations• Number - A number, characterized by its ordinality

and magnitude• Nil - A word without direct temporal meaning

Training Setup

• For each temporal phrase, a grammar tag is assigned .

• A total of 62 phrases are defined corresponding to instances of Ranges, Sequences, and Durations.

• 10 functions are defined for manipulating temporal expressions.

Training SetupGiven [ { (Phrase, Reference) , Time} ]Ex : { ( w1 w2 , 15-10-2013 ) , 22-10-2013 }w1 = next w2 =Tuesday

• Step 1: Get k-best parses for phrase( (next Tuesday , 15-10-2013 ) , 22-10-2013 )

• Step 2 : Filter and re-weight correct parses ( (next Tuesday , 15-10-2013 ) , 22-10-2013 )

• Step 3 : Update expected sufficient statistics

Feature Extraction

• Bracketed FeaturesEx:12th month of August 2013 can be realised as bracketed feature as <Intersect, Intersect ,12th>

• Lexical Featuresin the phrase for this week the Lexical Features extracted are <for,week>, <this,week> and <for this,week>

Drawbacks• Pragmatic Ambiguity - this week parsed as next

week or whether next weekend refers to the coming or subsequent weekend

• Semantic Errors – February the 30th or Friday the 13th this year

• Bad Reference Time - Assuming that the reference time of an utterance is the publication time of the article

References

• Language-Independent Discriminative Parsing of Temporal Expressions - Gabor Angeli, Jakob Uszkoreit

• Parsing Time: Learning to Interpret Time Expressions -Gabor Angeli, Chris Manning, Dan Jurafsky

• Hierarchical phrase-based translation. - David Chiang