Querying rich text with XQuery
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The document discusses Lux, an open source project that allows querying XML documents stored in Lucene using XQuery. Lux indexes XML documents while maintaining their tag structure and context. It supports both precise XPath queries and more general searches over tagged text using contextual indexes. Lux can be used for complex queries over semi-structured data, content analysis, and building applications with an XQuery backend.
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Querying rich text with XQuery
- 1. Querying Rich Text with Lucene XQuery { Michael Sokolov Senior Architect Safari Books Online
- 2. ! Overview of Lux ! Why we need want a rich(er) query language ! Implementation Stories ! Indexing tagged text ! Storing documents in Lucene ! Lazy searching ! Demo The plan for this talk
- 3. ! XQuery in Solr ! Query optimizer ! Efficient XML document format ! XQuery function library ! as a Java library (Lucene only) ! as Solr plugins ! as a standalone App Server What is Lux?
- 5. Query to get an answer
- 6. ! ! ! ! ! maybe it was once – 10 year s ago? Legacy stuff: DTDs, namespaces, etc arcane Java programming interfaces Don’t we use JSON now? so why do we care about it? XML is not cool
- 7. ! There’s a huge amount of it out there ! HTML is XML, or can be ! Lux is about making it easy (and free) to deal with XML But it still maZers
- 8. ! We make content-‐‑rich sites: ! our own site: safaribooksonline.com ! our clients sites: oed.com, degruyter.com, oxfordreference.com, … ! Publishers provide us with content ! we debug content problems ! we add new features nimbly ! Piles of random data (XML, mostly) Why did we make it?
- 9. ! Complex queries over semi-‐‑structured data, typically documents ! You don’t need it for edismax-‐‑style “quick” search ! or highly-‐‑structured data ! XQuery comes with a rich function library; ! rich string, numeric and date functions ! extensions for HTTP, filesystem, zip How can XQuery help?
- 10. DispatchFilter UpdateProcessor XML Indexer XML text fields Tagged TokenStream XPath fields Tinybin storage External Field Codec QueryComponent QParserPlugin Evaluator Saxon XQuery XSLT Processor XQuery Function Library Lazy Searcher ResponseWriter Compiler Optimizer Tagged Highlighter How does Lux work?
- 11. ! “hamlet” ! “hamlet” in //title ! “hamlet” in //scene/title, //speaker, etc… ! XQuery, but we need an index ! DIH XPathEntityProcessor ! But are XPath indexes enough? XML is text with context
- 12. ! In which speeches does Hamlet talk about poison? ! +speaker:Hamlet +line:poison ! Works great if we indexed speaker and line for each speech ! What if we only indexed at the scene level? ! What if we just indexed speech text as a field? ! XPath indexes are precise and fine-‐‑grained ! Great when you know exactly what you need How do we index context?
- 13. <play> <title>Hamlet</title> <act act=”1”> <scene act=”1” scene=”1”> <title>SCENE I. Elsinore ... </title> Index Values Tags title, act, @act Tag Paths /play, /play/title, /play/act, /play/act/@act Text hamlet, scene, elsinore Tagged Text play:hamlet, title:hamlet, @act:1 XPath user-‐defined Xpath 2.0 expression; eg: count(//line), replace(//title, 'SCENE|ACT S+','') Contextual Indexes
- 14. ! Tagged Text, Path index ! Imprecise, generic indexes, but more context than just full text ! XQuery post-‐‑processing to patch over the gaps ! Query optimizer applies indexes ! For when you don’t want to sweat the details: ad hoc queries, content analysis and debugging General purpose indexes
- 15. <scene><speech> <speaker>Hamlet</speaker> <line>To be or not to be, … </line> … scene speech speaker … scene speech line … scene speech line Hamlet To be ! ! ! ! Zext:scene:hamlet pos=1 Zext:speech:hamlet pos=1 Zext:speaker:hamlet pos=1 Zext:scene:to pos=2 Zext:speech:to pos=2 … Tokens emiZed Wraps an existing Analyzer (for the text) Responds to XML events (start element, etc) Maintains a tag name stack Emits each token prefixed by enclosing tags TaggedTokenStream
- 16. ! XPath: //speech[speaker=“Hamlet”][contains(.,”poison”)] ! “optimized” XQuery: lux:search(“+<speaker:Hamlet +<speech:poison”) //speech [speaker=“Hamlet”] [contains(.,”poison”)] ! Lucene Query: tagged_text:(+speaker:Hamlet +speech:poison) TagQueryParser
- 17. ! Generic JSON index ! Overlapping tags (part-‐‑of-‐‑speech, phrase-‐‑labeling, NLP) ! citation classification w/probabilistic labeling ! One stored field for all the text makes highlighting easier ! One Lucene field means you can use PhraseQuery, eg: PhraseQuery(<speaker:hamlet <speech:to) finds all speeches by hamlet starting with “to”. Tagged token examples
- 18. ! ! ! ! ! ! stored document = 100% qnames = +1.3% paths = +2.4% text tokens = 18% tagged text (opaque) = 18% tagged text (all transparent) = 71% What’s the cost?
- 19. subsequence( for $doc in collection()[.//SPEAKER=“Hamlet”] order by $doc/lux:key(“title”) return $doc, 1000, 20) subsequence ( lux:search(“<SPEAKER:Hamlet”, “title”, 1000) [.//SPEAKER=“Hamlet”] , 1, 20) Query optimization
- 20. ! Lux uses Lucene as its primary document store ! Lux tinybin (based on Saxon TinyTree) storage format avoids XML parsing overhead ! Experimental new codec stores fields as files Document storage
- 21. ! Problem: “big” stored fields ! Text documents get stored for highlighting ! Take time to copy when merging ! Can we do beZer by storing as files, but managing w/Lucene? “Big” binary stored fields
- 22. large stored fields small stored fields ExternalFieldCodec
- 23. ! Real-‐‑time deletes ! Track deletions when merging ! Keep commits with IndexDeletionPolicy ! Delete unmerged (empty) segments ! Off-‐‑line deletes ! Cleanup tool traverses entire index Deleting is complicated
- 24. ! ! ! ! 2-‐‑3x write speedup for unindexed stored fields a bit slower in the worst case But, text analysis can take most of the time Net: useful if you are storing large binaries Codec Performance (preliminary)
- 25. ! custom DispatchFilter provides: ! HTTP request/response handling in XQuery ! file uploads, redirects ! Ability to roll your own: cookies, authentication ! Rapid prototyping, testing query performance, relevance, in an application seZing App Server
- 26. ! Yes, but did you remember to index all the fields you need in advance? ! Yes, but did you want to format the result into a nice report *using your query language*? ! Yes, but did you want access to a complete XPath 2.0 implementation in your indexer? Isn’t Solr enough?
- 27. ! Find some sample content with a new tag we need to support ! Perform complex updates to patch broken content ! Troubleshoot content ! Explore unfamiliar content ! Write prototypes and admin tools entirely in HTML, JS and XQuery ! Demo: hZp://localhost:8080 Example uses
- 28. ! Downloads and Documentation at hZp://luxdb.org ! Source code at hZp://github.com/msokolov/lux ! Freely available under OSS license (MPL 2) ! Contributions welcome ! Thank you, Safari Books! Thank You!