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Targeted Language Resources for the Digitisation of Historical Collections

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  • 1. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Targeted Language Resources for the Digitization of Historical Collections Annette Gotscharek, Ulrich Reffle, Christoph Ringlstetter, Klaus U. Schulz CIS, University of Munich JISC Workshop 2009, Bath, UK
  • 2. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Questions and Methods  For historical documents of a specific period: what kind of linguistic resources?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 2
  • 3. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 3
  • 4. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 0. CIS within IMPACT • (1) Text Recognition: Adaption of Optical Character Recognition to historical documents • (2) Resources Building: Enrichment of texts to Improve Information Retrieval (IR) on historical documents • (3) Research beyond IMPACT: steps to a next generation interface to access collections of historical documents
  • 5. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 5
  • 6. 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. Special Challenges for the Digitization of Historical Materials 1500 1600 1700 1800 1900 • Imaging Damages on Originals • Optical Character Recognition Rate of Recognition Errors • Information Retrieval Historical Variants • Human Reading Unknown Words date footertext
  • 7. 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-
  • 8. 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 / daßwt IhroKhurftrstl Durchl gnädiglsterHcttVatterinderpictcr rndFrombkcltallmFürstenvorzusetzen!scyn/vnd das halst> in^cclcQ^ vci pluz^uäzn 5accr6o5 daß tl iN KilchkN GottW wehr als ein Priester .
  • 9. 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 ^.uglltt. schreibet/ (3) severe word segmentation errors vndExcmpelFürstl-vnd HeroischerTuzenF OCR on Gothic materials: good (WER < 10%); medium (10-30%); bad (< 30%)
  • 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. Why is it so bad (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
  • 11. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. IR: Search Problem even for keyed collections Kreüter ? krauter Kräuter (Eng herbs) kreuter 0 Results for Kreuter creuther – kräuter (= Engherbs) as kraͤuter, kreuter, kreüter, kreuter, creuther
  • 12. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 kraͤuter, 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 12
  • 13. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Language Resources to tackle challenges encountered in OCR and IR • 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 date footertext
  • 14. 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
  • 15. 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
  • 16. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Language in a historical corpus for German Modern lexicon (CISLEX): coverage on Main Corpus on 10 periods
  • 17. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Language in a historical corpus for German Compounds (modern components); coverage on Main Corpus on 10 periods
  • 18. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 18
  • 19. 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: 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 19
  • 20. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Modern lexicon Inflected Lemmatizing forms information … … teile teil (= part) ... teilen (= to share) taille taille (= waist) fragte fragen (= to ask) … … 20
  • 21. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure ~ 140 Modern lexicon Patterns Inflected Lemmatizing … forms information th → t … … ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 21
  • 22. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information th → t … … theile ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 22
  • 23. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information th → t … … theile ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 23
  • 24. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information th → t … … theile ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 24
  • 25. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information th → t … … theile ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 25
  • 26. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information th → t … … frug ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 26
  • 27. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Approximate matching procedure Spelling ~ 140 Modern lexicon variation Patterns Inflected Lemmatizing … forms information ? th → t … … frug ei → ai teile teil (= part) ey → ei ... teilen (= to share) l → ll taille taille (= waist) … fragte fragen (= to ask) … … 27
  • 28. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 28
  • 29. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Language in a historical corpus for German Hypothetical lexicon; coverage on Main Corpus on 10 periods
  • 30. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Manually collected special lexica Spelling Modern lexicon variation Inflected Lemmatizing forms information theile … … teile teil (= part) ... teilen (= to share) frug taille taille (= waist) fragte fragen (= to ask) … … 30
  • 31. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Manually collected special lexica Spelling Manual Modern lexicon variation mapping Inflected Lemmatizing forms information theile … … teile teil (= part) ... teilen (= to share) frug taille taille (= waist) fragte fragen (= to ask) … … 31
  • 32. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 32
  • 33. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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? 33
  • 34. 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 built 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)
  • 35. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Evaluation of OCR Results  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
  • 36. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 16th century 18th century 19th century Reduction Reduction Reduction Dictionary No. of word No. of word No. of word of error rate of error rate of error rate errors errors errors No Lexicon 1306 - 827 - 2074 - Optimal 756 42% 395 52% 612 70% Lexicon Modern 1096 16% 501 39% 888 57% Lexicon W.Historical 938 28% 481 42% 856 59% Lexicon Modern + 1011 25% 480 42% 849 59% Virtual H.L. WER > 50% WER ~ 10% 36
  • 37. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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. 37
  • 38. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Main insights IR experiment  18th and 19th century: – Pure matching approach leads to good precision values. – Recall values are acceptable 38
  • 39. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 39
  • 40. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. Answer to our refined Question Is 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 40
  • 41. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 41
  • 42. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 42
  • 43. IMPACT is supported by the European Community under the FP7 ICT Work Programme. The project is coordinated by the National Library of the Netherlands. 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 Liguistic Database lexicon for VD16 Improve IR access with a normalization lexicon 43
  • 44. 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