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Managing XML and Semistructured Data

Managing XML and Semistructured Data. Lecture 19: Compressing XML Data. Prof. Dan Suciu. Spring 2001. In this lecture. XML Compression Motivation XMill approach and results Resources XMILL: An Efficient Compressor for XML Data by Liefke and Suciu, in SIGMOD'2001.

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Managing XML and Semistructured Data

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  1. Managing XML and Semistructured Data Lecture 19: Compressing XML Data Prof. Dan Suciu Spring 2001

  2. In this lecture • XML Compression • Motivation • XMill approach and results Resources • XMILL: An Efficient Compressor for XML Data by Liefke and Suciu, in SIGMOD'2001

  3. Compression: The Problem • XML for exchange (space or time) • but XML is verbose • users prefer application specific formats: • Web Server Logs • EMBL • G2 • is XML doomed to fail ?

  4. An Example:Web Server Logs ASCII File 15.9 MB (gzipped 1.6MB): 202.239.238.16|GET / HTTP/1.0|text/html|200|1997/10/01-00:00:02|-|4478|-|-|http://www.net.jp/|Mozilla/3.1[ja](I) <apache:entry> <apache:host> 202.239.238.16 </apache:host> <apache:requestLine> GET / HTTP/1.0 </apache:requestLine> <apache:contentType> text/html </apache:contentType> <apache:statusCode> 200</apache:statusCode> <apache:date> 1997/10/01-00:00:02</apache:date> <apache:byteCount> 4478</apache:byteCount> <apache:referer> http://www.net.jp/ </apache:referer> <apache:userAgent> Mozilla/3.1$[$ja$]$(I)</apache:userAgent> </apache:entry> XML-ized inflates to 24.2 MB (gzipped 2.1MB):

  5. XMill • specialized compressor for XML data • makes XML look “small” • Download: • Now: www.research.att.com/sw/tools/xmill • Soon: www.cs.washington.edu/homes/suciu/XMILL

  6. How Xmill Works: Three Ideas Compress the structure separately from the data: gzip Structure gzip Data 202.239.238.16 GET / HTTP/1.0 text/html 200 … <apache:entry> <apache:host> </apache:host> . . . </apache:entry> =1.75MB +

  7. How Xmill Works: Three Ideas Group the data values according to their types: gzip Structure gzip Data1 gzip Data2 <apache:entry> . . . </apache:entry> 202.23.23.16 224.42.24.55 … GET / HTTP/1.0 GET / HTTP/1.1 … =1.33MB + +

  8. =0.82MB gzip Structure + gzip c1(Data1) + gzip c2(Data2) + ... How Xmill Works: Three Ideas Apply semantic (specialized) compressors: • Examples: • 8, 16, 32-bit integer encoding (signed/unsigned) • differential compressing (e.g. 1999, 1995, 2001, 2000, 1995, ...) • compress lists, records (e.g. 104.32.23.1  4 bytes) • Need user input to select the semantic compressor

  9. XML Compression

  10. Compression Tradeoff

  11. Summary of XML Data Management • XML = • old data type (trees) • with new interpretation (data) • We discussed traditional management techniques for XML: • Data model • Query language • Optimizations • ... • Many traditional problems still unsolved (storage, processing, optimization, ...)

  12. Summary of XML Data Management • More interesting question: • what are the novel applications enabled by XML ? Some ideas: • Approximate queries over unfamiliar data instances • “Search the database for a pattern similar to this one” • Rank results based on their similarity to the pattern • What is an appropriate query language for that ? • Linking independent databases • We have Xlink, how do we use it ?

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