Upload
emma-huber
View
840
Download
2
Embed Size (px)
Citation preview
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
JISC Workshop 2009, Bath, UK
Targeted Language Resources for the Digitization of Historical Collections
Annette Gotscharek, Ulrich Reffle, Christoph Ringlstetter,
Klaus U. Schulz
CIS, University of Munich
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
2
Questions and Methods
For historical documents of a specific period: what kind of linguistic resources?
What kind of improvements can be expected? Consequences for engeneering and processes?
---------------------------------------------------------------------- (1) Corpus analysis (2) Quantitative Experiments on OCR and IR
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
3
Survey
1. Special Challenges to Digitize Historical Materials 2. Composing and Analyzing a Historical Corpus 3. Types of Linguistic Resources 4. Evaluation of Benefits: OCR, IR 5. Consequences for Engineering
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
• (1) Text Recognition: Adaption of Optical Character Recognition to historical documents
• (2) Resources Building: Enrichment of texts to Improve Information Retrieval (IR) on historical documents
• (3) Research beyond IMPACT: steps to a next generation interface to access collections of historical documents
0. CIS within IMPACT
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
5
Digitization Projects for Historical Materials
SELECT Create a Historical Collection
SCAN Create Images: Greyscale, Color, QA
PROCESS Improve Images
OCR/Type Create a Symbolical Representation, QA
INDEX Process a Term-Document Representation
PRESENT Provide a User Interface for Access
date footertext
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
1500 1600 1700 1800 1900
• Imaging Damages on Originals• Optical Character Recognition Rate of Recognition Errors• Information Retrieval Historical Variants
• Human Reading Unknown Words
1. Special Challenges for the Digitization of Historical Materials
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Optical Character Recognition: Gothic, good quality
Städte den römischen mumcizmg gleich zu stellen. Allem wenn sich je in einem Rechtstheile die altrechtlichen teutschen Gewohnheiten, und Gesetze erhalten haben, so ist es gewiß in dieser Lehre, man mag entweder auf die Befugniß, die Stadtgerechtigkeit zu ertheilen , oder auf die innere Regimentsverfftssung so-
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Optical Character Recognition: medium quality
Fürsten zu Gstternwerden/wer wollte vermainen / daßwtIhroKhurftrstl Durchl gnädiglsterHcttVatterinderpictcrrndFrombkcltallmFürstenvorzusetzen!scyn/vnd das halst> in^cclcQ^ vci pluz^uäzn 5accr6o5 daß tl iN KilchkN GottW wehr als ein Priester.
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Examples of Noise introduced by imperfect OCR (1) processed word images may lead to False Friends Fischerei - Tischlerei: F->T, h -> hl (Engfishery - carpenterry)(2) processed word images may relate to no word at all
(3) severe word segmentation errors
OCR on Gothic materials: good (WER < 10%); medium (10-30%); bad (< 30%)
vndExcmpelFürstl-vnd HeroischerTuzenF
^.uglltt. schreibet/
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
(1) The image quality is challenging, further processing needed
(2) The classifiers of the OCR disregard certain type faces used in historic print
(3) The language resources of the OCR are inappropriate: historical language
Why is it so bad
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
– kräuter (= Engherbs) as kra uter, kreuter, kreüter, kreuter, creutherͤ
Kräuter
krauter
Kreüter
kreuter
creuther
?
0 Results for Kreuter
IR: Search Problemeven for keyed collections
(Eng herbs)
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
12
Special challenge for IR and OCR on historical Texts: Spelling variation Missing normalization of orthography leads to plenty
of spelling variants in historical documents, e.g. in German texts (1500-1850):– teil (= Engpart) as theil, teyl, theyl
– kräuter (= Engherbs) as kra uter, kreuter, kreüter, ͤkreuter, creuther
– fragte (= Engasked) as frug, fruk User is not aware of the variants and misses many
documents: sometimes even false friends Solution: Mapping from variants to modern lemma
date footertext
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
• Lexica for OCR• Language Models for OCR • Statistical Information about transformation patterns• Historical Stopwords for IR• Normalization Lexica with a mapping between modern and historical wordform for IR• Syntactical Information for paradigmatic expansion and disambiguation at POS level
Language Resources to tackle challenges encountered in OCR and IR
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Mantra: All Language Resources are Corpus Based
Possible sources:
• Keyed Materials on the Web
• Non Public Electronic Corpora
• Keying/corrected OCR of Image Corpora
• Noisy OCR Corpora
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Status of German historical Corpora
1. Main development corpus •Proofread texts from 1400 to 1900, •Medium size: 2.7 Mill. tokens •For lexicon construction•For diachronic analysis/classification of vocabulary of distinct periods
2. OCR corpus for lexicon testing•OCRed Images + groundtruth aligned•Texts from 16th, 18th, 19th century (5034, 2659, 18052) tokens
3. IR test corpus for lexicon testing•Special linguistically annotated groundtruth•Texts from 16th, 17th, 18th, 19th century 31080 tokens
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Modern lexicon (CISLEX): coverage on Main Corpus on 10 periods
Language in a historical corpus for German
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Compounds (modern components); coverage on Main Corpus on 10 periods
Language in a historical corpus for German
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
18
Two Variants of Lexica for IR and OCR
Hypotetical Lexicon: Trying to map input strings to modern lexicon entries in a dynamic way via a special approximate matching procedure using historical transformation patterns.
Witnessed Lexicon:Corpus checked lexicon entries:
Historical spelling variant + modern Lemma for IR
Historical word list for OCR
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
19
Hypothetical Lexicon: approximate matching procedure Many of the spelling variations can be traced back to
a modern word by applying characteristic patterns / rewrite rules– e.g. the historical string theyle can be traced to
its modern equivalent teile by applying th → t and ey → ei.
Required resources:– Contemporary lexicon with inflected word forms– Set of typical language-specific spelling variation
patterns
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
20
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
21
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
22
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
theile
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
23
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
theile
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
24
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
theile
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
25
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
theile
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
26
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
frug
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
27
Approximate matching procedure
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
~ 140 Patterns
…
th → t
ei → ai
ey → ei
l → ll…
Spelling variation
?
frug
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
28
Approximate matching procedure Advantages:
– No manual work needed
– Dynamic approach
Limitations:– Mismatches may link a historical spelling
variation to a wrong modern word.– A part of the historical vocabulary cannot be
reduced to a modern word by simple matching
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Hypothetical lexicon; coverage on Main Corpus on 10 periods
Language in a historical corpus for German
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
30
Manually collected special lexica
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
Spelling variation
theile
frug
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
31
Manually collected special lexica
Modern lexicon
Inflected forms
…
teile
...
taille
fragte
…
Lemmatizing information
…
teil (= part)
teilen (= to share)
taille (= waist)
fragen (= to ask)
…
Spelling variation
theile
frug
Manual mapping
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
32
Manually collected special lexica Advantages:
– Associations between historical variant and modern lemma are safe
– Associations that are not covered by the matching approach can be stored explicitly
Limitations:– Time consuming, labor-intensive, situations
occur where specialists (historical linguists) are needed.
– Hardly ever complete because of immense number of spelling variants
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
33
Evaluation of the approximative matcher – is the lexicon redundant?
Few empirical studies on crucial decisions for IR and OCR on historical texts:– Is a matching approach enough?
– Do we need a lexicon, and if so, in which scenarios?
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
both assign modern lemmas to historical full forms
Validated lexicon constructed from Main Corpus
currently ca. 15,000 entries (“kernel lexicon for hist. German”) poor coverage
Witnessed lexicon for OCR: from Main corpus, 200,000 tokens without modern correspondence still limited coverage: corpus size
Hypothetical lexicon for IR”: matching procedure mapping historical full form to modern pendant plus lemmatizer for modern language (historical full form <---> modern lemma), based on 140 patterns theoretically 100 Mio entries. High coverage, assignments can be erroneous, only able to capture regular correspondences (pattern based)
Lexica built
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Test Corpus for 16th , 18th , and 19th century Development version of a professional OCR engine with an external
dictionary interface Experiments with different lexicon settings
No additional lexicon, character model only German modern lexicon corpus based witnessed lexicon hypothetical lexicon
Evaluation of OCR Results
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
36
Dictionary16th century No. of word
errors
Reduction of error rate
18th century No. of word
errors
Reduction of error rate
19th century No. of word
errors
Reduction of error rate
No Lexicon 1306 - 827 - 2074 -
Optimal Lexicon 756 42% 395 52% 612 70%
Modern Lexicon 1096 16% 501 39% 888 57%
W.Historical Lexicon 938 28% 481 42% 856 59%
Modern + Virtual H.L. 1011 25% 480 42% 849 59%
WER > 50% WER ~ 10%
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
37
Evaluation of the approximate matcher in an IR scenario
proofread documents from 16th, 17th, 18th and 19th century and tagged each token manually.
Collected a list of historical) stopwords Defined “precision” and “recall” for our scenario.
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
38
Main insights IR experiment
18th and 19th century:– Pure matching approach leads to good
precision values.– Recall values are acceptable
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
39
Main insights IR experiment
16th and 17th century:– Precision of the matching approach poor, a
lexicon will help to avoid wrong matches.– Recall values show that a large number of words
can only be explained by a special lexicon
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
40
Answer to our refined QuestionIs the lexicon redundant for OCR/IR on historical
texts? Depends on the material, especially on the date of
origin of the collection:– Matching approach leads to acceptable results for 19th
and 18th century collections.– Serious limitations for 16th and 17th century collections.
Special lexica will lead to important improvements
Combination of matching approach and manually collected lexica may lead to optimal results.
For postprocessing validated lexica are needed
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
41
Engineering Consequences
A Focus Collection of the BavarianStateLibrary
VD16: Collection of Early High German Books
Collaborative project with BSB on OCR/IR for this collection: Clemens Neudecker/Fedor Bochow
Special lexicon building needed No 16th century electronic corpora available for
lexicon development For real world test we defined a topic area as main
interest: Theology
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
42
Engineering Consequences
Iterative Process with Bavarian State Library to Create Resources for VD16 Collection
(1) A random selection of 200 pages from 100 sources
(2) OCR and corpus experiments
(3) Selection of usable sources
(4) Specification of keying by BSB/CIS for 70 complete books usable for both presentation and linguistic resources building
(5) Contract with service providers
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
43
Engineering Consequences
A Focus Collection of the BavarianStateLibrary
VD16: Collection of Early High German Books with 30 million pages
Integrate OCR Supplier: Special Type Face
Models; Character Models
Improve OCR with a specialized historical
lexicon
Improve IR access with a normalization lexicon
Liguistic Database
for VD16
IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands.
Wrap Up• For challenging historical materials specialized
lexica are needed
• Special lexica directly implemented into basic OCR lifts OCR quality significantly. For bigger projects seek direct collaboration with OCR partners
• For IR: use approximative matching or normalization lexica to process user queries
• Integrate research institutions and collection holders