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Beyond Text Representation

Beyond Text Representation. Building on Unicode to Implement a Multilingual Text Analysis Framework Thomas Hampp – IBM Germany Content Management Development. Basic Text Analysis Tasks. Code page conversion and text re presentation Segmentation (tokens, sentences, paragraphs)

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Beyond Text Representation

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  1. Beyond Text Representation Building on Unicode to Implement a Multilingual Text Analysis Framework Thomas Hampp – IBM Germany Content Management Development

  2. Basic Text Analysis Tasks • Code page conversion and text representation • Segmentation (tokens, sentences, paragraphs) • Morphological analysis / dictionary lookup • Compound word decomposition • Spell Checking/Spell Aid • … 18th International Unicode Conference

  3. Advanced Text Analysis Tasks • Summarization • Categorization/Clustering • Extraction of names, terms or relations • Information extraction • Parsing All task should be provided for all languages 18th International Unicode Conference

  4. A Library for Text Analysis • The same text analysis tasks are needed in different multilingual contexts/systems • The same software library should be used in all contexts/systems to perform the analysis • The library should work language neutral • The text analysis tasks required for a given context/system should be an input parameter for the library 18th International Unicode Conference

  5. Two Problems and One Solution • The realization of such a library faces two kinds of challenges: • Implementing the actual language specific analysis tasks • Encapsulating the language specific processing by representing input and output in a language neutral fashion • Unicode plays a major role in solving problem B 18th International Unicode Conference

  6. A Software Design for a Text Analysis Library • Single API towards the application • Separated but combinable language-specific processing modules • Central representation system for linguistic information • Centralized flow of control driven by linguistic analysis targets 18th International Unicode Conference

  7. Implementation • Implemented as C++ DLL/shared Lib • Provides an extensive object oriented API for applications and plugins • Uses Unicode (ICU based) for all text content • Ported to 9 platforms (therefore no platform dependant solutions acceptable) • Because of use in search/indexing strong focus on performance • Supports 30+ languages and 90+ code pages 18th International Unicode Conference

  8. Enter Unicode • Used as internal character representation format (character set) • Converters from/to over 90 external code pages had to be written/integrated • A decision had to be made on the Unicode encoding format: we choose UTF-16 18th International Unicode Conference

  9. The Pros UTF-16 • We started out without knowledge of surrogate issues • False assumption: Fixed length encoding • Good balance between size and straightforward representation • Efficient interoperability with Windows, Java, XML4C APIs etc 18th International Unicode Conference

  10. The Cons of UTF-16 • Not a fixed length encoding because of surrogates • Can not be passed to legacy functions (C library, OS APIs) • Character classification functions have to work on pointers for surrogates • Wastes some space with western languages 18th International Unicode Conference

  11. ANSI C/C++ Compatibility • ANSI C++ does define a type w_char for “wide” character representation (and a matching wide string class wstring) • Unfortunately size and encoding of w_char are not standardized • So we combined the ANSI C++ basic_string template class with the Unicode character data type from ICU to create a C++ and Unicode conformant string class 18th International Unicode Conference

  12. Impact Beyond Character Representation • Tokenization • Finite state processing • Dictionary formats • “Environmental” issues • Development tools support 18th International Unicode Conference

  13. Impact: Tokenization • Tokenization needs access to character properties • Most but not all relevant are provided by Unicode character database • For application defined properties there is no more fast & simple 256 character property lookup • Approach limited to western scripts 18th International Unicode Conference

  14. Impact: Finite State Processing • Finite state character processing in C usually works with transition tables encoded as arrays • This is easy to implement and very fast in execution • To cover the full range of all Unicode characters, more sophisticated transition tables are required 18th International Unicode Conference

  15. Impact:Dictionaries • Dictionaries tend to be large • As much of them as possible has to be loaded in memory for performance reasons • For multilingual (server) applications multiple dictionaries will be in memory • Therefore dictionary size matters much • Doubling dictionary size might not be an viable option 18th International Unicode Conference

  16. Impact: “Environmental” Issues • There is always as residue of single byte string data (from message catalog, command line, library calls etc.) which sometimes has to be mixed with Unicode string data • Interfaces for console, messages, logs etc. are mostly single byte • Configuration files should be platform-neutral, easily editable and support the full Unicode character set 18th International Unicode Conference

  17. Impact: Development Tools Support • Only specialized editors can handle Unicode text • Most debuggers don’t display Unicode • Source code string constants are hard to maintain • Message catalog compilers on some platforms are not Unicode enabled 18th International Unicode Conference

  18. A Word About Unicode Normalization Forms • For reasons of efficient interoperability a fixed Unicode normalization had to be specified • Early normalization is performance critical • Since round trip convertibility was not a design goal Unicode Kompatibility Composed Normal Form has been chosen • Normalization and cope page conversion can and should be done in one step 18th International Unicode Conference

  19. Benefits of Unicode Use • No more code page troubles within the boundaries of the application • Very often algorithms can be established for groups of languages • Multilanguage document collections and even mixed language documents are no problem to represent • Easy and efficient Java (JNI) integration 18th International Unicode Conference

  20. Summing Up:Building on Unicode… • …solves only the basic character representation problem for multilingual text analysis • …sets a solid foundation for a multilingual system • …enables algorithms to be reused for groups of languages. • …can have impact on the system far beyond the character representation level • …has been worth the trouble 18th International Unicode Conference

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