A Splitter for German compound
words
Pasquale Imbemba
Free University of Bozen-Bolzano
Supervisor: Dr. Raffaella Bernardi
Scenario
User input
Compound words in German
●
Problem for IR
-retrieval of German books
-no direct keyword matching
●
Problem for CLIR
-retrieval of IT & EN books
-No direct translation in
dictionary
2
Problem: German compound words
Compounding is productive:
●

Combine pre-existing morphemes to form a new word (aka
Univerbierung)

Compounds of nouns most frequent cases
User input may not be in the lexicon used by CLIR search
engines

●
User input may be a lexicalized “compound” word

●
●
Donau + Dampf + Schiff + Fahrt
(tr.: Steam navigation on the Danube)
Malerei (tr.: painting) no: Maler+Ei (tr.: painter and egg)
Hence, need of a splitter to handle both cases
Furthermore, language is in continuous evolution (neologism);
need of constantly up-to-date lexical resources
3
State of the art
●
TAGH
(Berlin-Brandenburg Academy of Sciences / University
of Potsdam)

●
MORPHY

●
(University of Paderborn)
Reduce to base form and affixes, look them up
MORPA

●
Weighted FSA: choose combination with least cost
(Tilburg University)
Probabilistic calculus to determine segmentation
De Rijke/Monz

(University of Amsterdam)
Shallow approach
●
Given a word, if substring is in lexicon, subtract it. Repeat
until no substring is left.
4
Tools
●
Splitter

Mechanism to segment nouns
●
●
Implemented, evaluated and improved De Rijke/Monz
algorithm using Java
Lexicon

Morphy (57,000 nouns), dated (Lezius)

deWaC (440,000 nouns), recent (Baroni & Kilgarriff)
●
Lexical resource to execute lookup onto



Extracted nouns from Morphy & deWaC
Regular Expression filtering on deWaC
Resources indexed with Lucene
5
De Rijke/Monz algorithm
Split (word)
For i := 1 to length-1 do
if substring(0,i)isInNounLex && split(substr(i+1,length) != “ “ do
r = split(substr(i+1,length)
return concat (substr(1,i),+,r)
if (isInNounLex(word))
return word;
else
r = split(substr,i to length)
return ““;
Ö l
Ö l p r e i s
p r e i s
p r e i s
p r e i s
P r e i s
p r e i s
r = preis
6
Enhanced Splitter workflow
●
●
Cascading lexical
resources

Increases split correctness

Improves overall
correctness
Lookup first

Lexicalized elements

Reduces amount of
incorrect splits
7
Splitter diagram
8
MuSiL Integration
Query Input
Donaudampfschifffahrt
Name Recognition
Donau
Dampfschifffahrt
Morphological Analysis
Dampfschifffahrt_N
Multiword recognition
Dampfschifffahrt_N
Split and Translate
Multilingual Dictionary
EN: vapour_N | steam_N (...)
2
1
Splitter
3
EN: ship_N | (...)
EN: drive_N | navigation_N (...)
IT: vapore_nm | (...)
IT: nave_nf | (...)
IT: guida_nf | navigazione_nf (...)
Multilingual Thesaurus
9
Evaluation
De Rijke/Monz Splitter
Our Splitter
deWaC
Morphy
deWaC
Lexicon used
6.201
16.141
6.207
Total splits
2.723
4.851
2.022
Total non splits
3.478
11.290
4.185
Total NS wrong
1.322
50
1.404
Split due to lexical error
2.383
66
1.871
Split due to logic error
9
1.067
7
Correct splits
331
3.718
144
Split correctness
12,16%
76,64%
7,12%
Correct elements
2.487
14.958
2.925
Correctness
40,11%
92,67%
47,12%
●
Morphy
16.135
4.517
11.618
50
45
864
3.608
79,88%
15.176
94,06%
Total correctness improved
●
By increasing the amount of non splits with deWaC and Morphy
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Complexity of the split function
• De Rijke/Monz
– Best case:
• We scan the input word
from first to last position
T (n)  (n  1)  O(n)
– Worst case:
• Calls to split
• Exponential growth
n


1

2
i


T (n)   2  O
i 0
 1 2 
n 1
• Our splitter:
– Best case:
• We find the word
immediately to exist in the
lexical resources of nouns
T (n)  O1
– Worst case:
• Execute function
recursively every time we
encounter a word in the
lexicon and the remaining
substring is not empty (see
De Rijke/Monz)
11
Performance on MuSiL
Without splitter component
With splitter component
DE
IT
EN
Precision
DE
IT
EN
Precision
Abenteuer+Geschichten
1
0
0
100%
10
57
2
51%
Beruf+Orientierung
13
0
0
100%
13
392
24
43%
Kommunikation+Politik
-
-
-
-
28
69
317
47%
Wert+Papier+Handel+Gesetz
4
0
0
100%
0
36
90
17%
Doppel+Besteuerung+Abkommen
4
0
2
100%
0
0
15
100%
Aufmerksamkeit+Defizit+Syndrom
44
0
25
36%
3
0
8
73%
Hirn+Leistung+Training
15
0
0
100%
4
48
189
46%
Kunst+Erziehung+Bewegung
1
0
0
100%
144
478
251
36%
Emotion+Regulierung
1
0
0
100%
0
3
66
71%
Unternehmen+Netzwerke
8
0
25
61%
73
61
677
27%
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Increased amount of retrieved documents
●
More relevant documents are top ranked
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Conclusion and future work
●
●
Good:

Cascade method

Deal with lexicalized elements
Open topics:

Choose correct segmentation among alternatives

Metrics for correctness of segmentation
●
Weights, probability …
13