Building Natural Language Generation (NLG) Systems Ross Turner

Tomorrow’s Language Technology, Berlin 17/09/15

Agenda

1.  Brief introduction

2.  NLG in 10 minutes

3.  Case study: NLG in Weather Services

4.  Statistical approaches to NLG

5.  Where next?

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Who am I?

My Profile

•  Current: Principal Engineer, Arria NLG plc

•  Formerly:

–  Senior Software Engineer, Nokia Berlin

–  Post-doctoral Research Fellow, Universities of Edinburgh and Aberdeen

•  PhD in Applied NLG systems in 2009

4

��

What is � Natural Language Generation (NLG) �

exactly?�

��NLG Synopsis�� •  The automatic generation of natural language from non-linguistic input

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Input   Seman+c  Representa+on   Text  

Example

"Grass pollen levels for Wednesday have decreased from the very high levels of yesterday with values of around 6 to 7 across most parts of the country. However, in Northern and North Western areas, pollen levels will be moderate with values of 4. "

7 Turner  et.  al  2006  

��Reiter & Dale Pipeline Architecture��

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Choosing  What  to  Say  

Deciding  How  to  say  it  

��System Building�� •  Development requires example input data and corresponding output text

•  Systems are usually knowledge-based and domain-specific, but statistical approaches are becoming more commonplace

•  Evaluations typically use:

–  Automated metrics against a gold standard

–  Human ratings

–  Task-based evaluations

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�What about applications?

Commercial Applications

•  NLG Commercialisation has been relatively recent

•  Many systems developed in Healthcare, Meteorology, Finance etc.

•  Most common applications are so called “data-to-text” systems that provide decision support

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Benefits

•  Scalability, cost-efficiencies, automation of routine reporting etc.

•  Task-based evaluations have highlighted the benefits of textual presentations of data:

–  Medical staff made better decisions (Law et al. 2005)

–  Mobile phone users exhibited superior task performance (Langan-Fox et al. 2006)

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��

Can NLG produce high quality texts?�

Output Variation and Quality

•  NLG systems have been developed to generate:

–  Narrative Prose (Callaway 2002)

–  Poetry (Manurung 2003)

–  Jokes (Binsted and Ritchie 1994, Manurung et al. 2008)

•  SumTime-Mousam wind forecasts were judged better than those written by human experts (Reiter et al. 2005)

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Case Study: Weather Services

Road Ice Forecasts

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Input Data

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Input Data

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Input Data

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Communicative Goal

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System Output

Computer Generated Forecast

•  “Road surface temperatures will fall slowly during the afternoon and early evening, reaching zero in some northwestern places by 15:00. Ice and hoar frost will affect all routes throughout the forecast period, hoar frost turning heavy by 15:00 in some places below 100M. Fog will affect all routes throughout the forecast period, turning freezing by 16:00 in all areas.”

Human Authored Forecast

•  “A dry and settled night. It will be cold, despite rather cloudy skies at times and freezing fog is expected to form along the lower routes. Hoar frost will be widespread across the region and there will also be icy patches at some locations. RSTs are expected to fall to between minus one and minus three degrees.”

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Evaluation with Road Engineers

•  Online questionnaire:

–  Ask Road Engineers to rate pairs of road ice forecasts based on the same data

–  21 respondents, 17 with 5+ years experience.

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Experimental Setup

•  Gritting decision conditions:

–  Marginal Night? Yes (MN+), No (MN-)

–  Settled Conditions? Yes (SC+), No (SC-)

•  SC-MN-: Grit all routes

•  SC+MN-: Grit all routes

•  SC-MN+: Grit some routes

•  SC+MN+: Grit some routes

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Questions: Direct Comparisons

Q1 In terms of the information presented in both texts, which is most useful?

Q2 Which text do you find easier to understand?

Q4 Which text would allow you to prioritise the routing of gritting vehicles better?

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Results: Direct Comparisons

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Questions: Task-based

Q3 Please indicate for both texts roughly how many routes you would treat

(all, some or none)?

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Results: Task-based

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Meteorologists Beta Feedback

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•  Forecaster’s ratings vs forecaster’s post-edit behaviour

“Do as I say, not as I do”

Public Weather Forecasts

Sripada  et.  al  2014   29

Business Use Case

•  UK Met Office produces forecast data for 1000s of sites every 3 hours

•  Manpower dictates written forecasts can only be produced at the area level

•  Solution: develop a NLG system to generate site-specific weather forecasts

Sripada  et.  al  2014      

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Results obtained over 10 trials using a MacBook Pro 2.5 GHz Intel Core i5, running OS X 10.8 with 4GB of RAM

Sripada  et.  al  2014      

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Scalability

Output Quality

35 @metoffice followers:

1.  Did you find the text helped you to understand the forecast better?

–  Yes 97%, No 3%

2.  How did you find the text used?

–  About right 74%, Too short/long 20%, Unsure 6%

3.  Would you recommend this feature?

–  Yes 91%, No 9%

Sripada  et.  al  2014      

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��

Statistical Approaches To NLG�

��NLG Is All About Choice�� •  Choosing what to say and how to say it:

–  Content

–  Words

–  Syntactic structure

•  Many of these choices can be learnt:

–  Overgeneration and ranking

–  Word choice classifiers

–  Word ordering

Evaluating System Building Cost

•  Belz and Kow (2010) evaluated implementations of SumTime-Mousam

–  The original handcrafted version

–  Probabilistic Context Free Grammars (PCFG)

–  Statistical Machine Translation

•  Human ratings favoured the original handcrafted system while metrics favoured automated systems

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�Some Discussion of Statistical Approaches� •  Statistical approaches can replicate a corpus well and reduce system

building cost

•  Hybrid statistical approaches have the potential to support domain adaptability (Kondadadi et al. 2013)

•  Uncertain how to refine the output of model based systems

•  Large amounts of aligned training data is normally required

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Recap

The Story So Far…

•  NLG systems can produce high quality texts

•  NLG systems solve business problems

•  Statistical NLG approaches are still evolving

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Where Next?

Robot Journalism

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�Deep Learning�

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�The Future?� •  New learning and statistical models

•  Domain independence

•  Multilinguality

•  Targeted web content

•  Big data analysis

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Thank you

References •  Belz A. and Kow E. (2010), Assessing the Trade-Off between System Building Cost and Output Quality in Data-to-Text Generation. In

Krahmer, E., Theune, M. (eds.) Empirical Methods in Natural Language Generation, Vol. 5980 of Lecture Notes in Computer Science, Springer, pp. 180-200.

•  Binsted K. and Ritchie G. (1994) An Implemented Model of Punning riddles. In Proceedings of the Twelfth National Conference on Artificial Intelligence (AAAI-94).

•  Callaway, C. B. and Lester, J. C. (2002). Narrative prose generation. Artificial Intelligence, 139(2):213–252.

•  Kondadadi R., Howald B. and Schilder F. (2013) A Statistical NLG Framework for Aggregated Planning and Realization. In ACL (1), 1406-1415

•  Law A., Freer Y., Hunter J., Logie R., McIntosh N. and Quinn J. (2005). A Comparison of Graphical and Textual Presentations of Time Series Data to Support Medical Decision Making in the Neonatal Intensive Care Unit. Journal of Clinical Monitoring and Computing 19 (3): 183–94

•  Langan-Fox, J., Platania-Phung, C. and Waycott, J. (2006). Effects of advance organizers, mental models and abilities on task and recall performance using a mobile phone network. Applied Cognitive Psychology, 20(9):1143-1165

•  Manurung, R., Ritchie, G., Pain, H., Waller, A., O’Mara, D., and Black, R. (2008). The construction of a pun generator for language skills development. Applied Artificial Intelligence, 22(9):841–869.

•  Reiter, E., Sripada, S., Hunter, J., Yu, J., and Davy, I. (2005). Choosing words in computer- generated weather forecasts. In Artificial Intelligence, volume 67, pages 137–169

•  Sripada S. Burnett N., Turner R., Mastin J. and Evans D. (2014). A Case Study: NLG meeting Weather Industry Demand for Quality and Quantity of Textual Weather Forecasts. In proceedings of INLG-2014, Philadelphia, PA, USA, 19-21.

•  Turner R., Sripada S., Reiter E. and Davy I. (2006). Generating Spatio-Temporal Descriptions in Pollen Forecasts. EACL-06proceedings, Trento, Italy, April 3-7.

•  Turner, R. (2009) Georeferenced data-to-text : techniques and application. Ph.D Thesis, University of Aberdeen. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509142

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Images •  “Snowwiper near Toronto, Canada”, by Jkransen, CC BY-SA 2.5 – Slide 15

•  "John's Weather Forecasting Stone”, by Tim Rogers, CC BY-NC-SA 2.0 – Slide 28

•  http://googleresearch.blogspot.de/2014/11/a-picture-is-worth-thousand-coherent.html - Slide 36

•  http://www.theguardian.com/media/shortcuts/2014/mar/16/could-robots-be-journalist-of-future - Slide 40

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