1 2 2Copyright © 2019 Shohei Tanaka All Rights Reserved

2/37

Neural Conversational Model (NCM)
<eos>

RNN

<sos>

NCM [Vinyals et al., 2015]?


 %#$ ' "
& !
Copyright © 2019 Shohei Tanaka All Rights Reserved



3/37

;4-5269.=;4-52 NCM +1'&))

 69:8

03



%


7 ,!"$!#(!>→*<;4-5/69.=Copyright © 2019 Shohei Tanaka All Rights Reserved

4/37

e.g.
Why-QA  [Oh et al., 2013] 2Copyright © 2019 Shohei Tanaka All Rights Reserved

5/37

+"#/($*. % /($*+"#.

$* &1, → 0 $*1,  -!'→ ) 
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6/37   

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7/37

""4(1

1. 
2. #
3. NCM%)52

,/01. 
2. 
3. #

2
""
'.

""
,/0-1*&+
e.g. !6
 $3Copyright © 2019 Shohei Tanaka All Rights Reserved

8/37  NCM

1.  
2.  
3. 1Copyright © 2019 Shohei Tanaka All Rights Reserved

9/37

A:2;8 *),",$
1

<?@=/B7*),",$
05FC

1. 
2. -05FC1A:2;6
3. NCM



<?@=

1. 
2. 
3. -2*),",$
4>*),",$<?@=

E→*)&#%
A:2;93

A:2;(!
(e.g. %'+%G .D)

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10/37-Copyright © 2019 Shohei Tanaka All Rights Reserved

11/37

(e( ((e.g.

→b)(()W

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&9'@-. 0 #<D>3+4!6*%

BC…

E…

)/F?$&9('@-.)>3+4
('@-.)
"G

…

…

(@…

…



5;=8$&9 ('@-.)<D,)/$E→  >3+4"G→(@ <D >3+4$ : 1A72
Copyright © 2019 Shohei Tanaka All Rights Reserved

13/37

Role Factored Tensor Model (RFTM) [Weber et al., 2018] !
 

…

T

W11+


T…

…

W22 Copyright © 2019 Shohei Tanaka All Rights Reserved

14/37



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15/37




NCM



EncDec, HRED

1-best (  ),/
260 Twitter ( 6)Copyright © 2019 Shohei Tanaka All Rights Reserved

16/37

Encoder-Decoder with Attention [Luong et al., 2015]
attention
Attention
hidden state vector)

Encoder, Decoder

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Hierarchical Recurrent Encoder-Decoder [Serban et al., 2016] (hierarchical)   utterance encoder  context encoder  Context Encoder
Utterance Encoder

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18/37 $)+&#(*%"
-!

!

NCM



EncDec12 %HRED
EncDec70 %HRED'- !
.,

#Copyright © 2019 Shohei Tanaka All Rights Reserved

19/37

!$(- .2• BLEU
#(- N-gram 0)

#(-&3%1(-&3%1,• NISTBLEU2 *4+"'

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/

20/37

• Vector Extrema(esewd)Copyright © 2019 Shohei Tanaka All Rights Reserved

21/37

BLEU, NIST, and extrema


NCM



BLEU

NISTextrema

1-bestEncDec 




1-best
HRED







 !

NCM !



1-best 

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22/37

&-)• Dist-1, 2
#( N-gram +#(&"'• Pointwise Mutual Information (PMI)#(*%#(-'Dist, PMI#(.,*%$!

Copyright © 2019 Shohei Tanaka All Rights Reserved

23/37

Dist and Pointwise Mutual Information (PMI)
NCM



dist-1

dist-2PMI

1-bestEncDec 
1-best
HRED  Copyright © 2019 Shohei Tanaka All Rights Reserved

24/37 

NCM

HREDv.s.


HRED + /



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25/37

2222

• Word coherency
02131• Dialogue continuity
02122

••2

1
Copyright © 2019 Shohei Tanaka All Rights Reserved

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Word Coherency
Coherency

28.62
0%

1-best

37.47

20%

40%

neither

33.91
60%

80%

100%

Re-ranking w/o embedding
Coherency

30.10
0%

1-best20%

neither

44.50
40%

60%

25.40
80%

100%

Re-ranking w/ embedding      
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27/37

Dialogue Continuity

Continuity

40.84
0%

1-best

20%

20.63
40%

neither

60%

38.53
80%

100%

Re-ranking w/o embeddingContinuity

35.50
0%

1-best20%

neither

26.30
40%38.20
60%

80%100%Re-ranking w/ embedding    

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28/37 •Word coherency •Dialogue continuity    (dist) ! (PMI)  

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29/37 

Copyright © 2019 Shohei Tanaka All Rights Reserved

30/37

(%5/( ()

26










19

26 + 19= 45

51%

5%5% %+)+0
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31/37

02 2)555   ()  (/)8

1445%

8 + 14= 2290)

02

2(Copyright © 2019 Shohei Tanaka All Rights Reserved

32/37

1



1



 (1-best)
 (Re-ranked)



1





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133/37

…

(1-best)
(Re-ranked)

2

Copyright © 2019 Shohei Tanaka All Rights Reserved34/37()

(1-best)((Re-ranked)(…

… …

3)

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35/37



Copyright © 2019 Shohei Tanaka All Rights Reserved

36/37

/&337

•

 #!

•"%

$Copyright © 2019 Shohei Tanaka All Rights Reserved