Oxpath vldb
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1. The document summarizes OXPath, a domain-specific language for extracting structured data from web applications through interactive queries. It describes OXPath's advantages over previous wrapper languages, including its use of XPath for navigation and extraction as well as support for interaction through imperative commands. 2. The document provides an example of an interactive OXPath query to extract flight information from the Kayak website. It demonstrates how OXPath allows specifying navigation steps and extraction markers to scrape relevant data across multiple pages. 3. Finally, the document argues that OXPath can serve as a "lingua franca" or common language for web extraction, addressing limitations of previous systems that each defined their own proprietary
![The nesting in the result mirrors the structure of the OX
pression: extraction markers in a predicate (title, source
sent attributes to the last marker outside the predicate (sto
Kleene Star. Finally, we add the Kleene star, as in [1
example, the following expression queries Google for “O
Seattle
traverses all accessible result pages and extracts all links.
doc("google.com")/descendant::field()[1]/{"Oxford"}
/following::field()[1]/{click /}
/( /descendant::a:<Link=(@href)>[.#="Next"]/{cli
To limit the range of the Kleene star, one can specify up
lower bounds on the multiplicity, e.g., (...)*{3,8}.
doc("zillow.com")/descendant::field()[1]/{"Seattle"}/fo
/descendant::input[@type=’checkbox’][2]/{uncheck}/follo
//div[.="Beds"]/following-sibling::select/{"3+"/}//a[./
9](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-9-320.jpg)
![The nesting in the result mirrors the structure of the OXPath ex-
pression: extraction markers in a predicate (title, source) repre-
sent attributes to the last marker outside the predicate (story).
Kleene Star. Finally, we add the Kleene star, as in [12]. For
example, the following expression queries Google for “Oxford”,
traverses all accessible result pages and extracts all links.
doc("google.com")/descendant::field()[1]/{"Oxford"}
/following::field()[1]/{click /}
/( /descendant::a:<Link=(@href)>[.#="Next"]/{click /} )*
To limit the range of the Kleene star, one can specify upper and
lower bounds on the multiplicity, e.g., (...)*{3,8}.
doc("zillow.com")/descendant::field()[1]/{"Seattle"}/following::*#GOButton/{
/descendant::input[@type=’checkbox’][2]/{uncheck}/following::field()[1]/{unc
//div[.="Beds"]/following-sibling::select/{"3+"/}//a[./text()="More filters"
//input[following-sibling[contains(.,"Multi Family")]]/{uncheck/}
/(//span.arrowNext/a/{click/})*//ul#search-results/li:<property>
[//div.property-info//a/{click/}//div.home-description:<info=(.)> 10
z](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-10-320.jpg)
![Start at kayak.co.uk:
doc("rightmove.co.uk")
To select an airport, type a few letters and select from completion list
//field().destination/{"Sea" /}
//div#smartbox//li[1]/{click /}
Submit the form
14](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-14-320.jpg)
![Refine the results by unchecking the “2+ stops”:
//*#stops2/{uncheck }
On all result pagesattributes
Extract the
/(//a[.=‘Next’]/{click /})* warnings
Mouseover the ! to extract flight quality
and//span.qualityWarningIcon/{mouseover /}
for each flight
//body.resultrow:<flight>
Click on the details to extract layovers
15](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-15-320.jpg)
![2 OXPath » The Language
Interactive Wrapper for Kayak
doc(‘‘kayak.co.uk’’)//input#origin/{“Lon” /}
//div#smartbox//li[1]/{click /}
//input#destination/{“Sea” /}
//div#smartbox//li[1]/{click /}
/descendant::field()[last()]/{click /}
//*#stops1/{uncheck }/following::*#stops2/{click /}
/(//a[.=’Next’])*
//body.resultrow:<flight>
[.//a.results_price:<price=string(.)>]
[.//span.qualityWarningIcon/{mouseover /}
//div.airqualitylist//tr:<warning=string(.)>]
[.//a.resultdetaillink/{click /}
//*.layover//td.airportCode:<layover=string(.)>]16](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-16-320.jpg)
![2 OXPath » The Language
➌ Iteration: Kleene Star
Most web sites use pagination for results
traversing paginated results require iteration
⇢ extraction from any unbounded component of a link graph
Kleene Star from Regular XPath [Marx TODS ‘05]
extended to OXPath, i.e., with action in the iterated expression
/(//a[.=’Next’])*
OXPath’s Page-at-a-time algorithm
buffers in practice only a constant number of pages
even for very large components
20](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-20-320.jpg)
![OXPath » Formal Properties
3
Semantics – Overview
Semantics defined over relational structure
as in XPath Leashed [Benedikt 08]
but: extended to multiple documents and with action relations
action relations form tree ⇢ no two actions lead to same DOM
but: instead of single node set, set of relations for extracted tree
Context extended by last match for parent extraction marker
necessary to construct the extraction tree
last match for sibling extraction used for
compact specification of records with mixed attributes and nested records
24](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-24-320.jpg)
![N1 J estep/path KN (c) = {c⇧⇧ | c⇧ ⌃ J estep KN (c) ⌦ c⇧⇧ ⌃ J path KN (c⇧ )}
N2 J axis::nodes KN (c) = { n⇧ , c.p, c.l | Raxis (c.n, n⇧ ) ⌦ n⇧ ⌃ Rnodes }
N3 J step[q] KN (c) = {c⇧ ⌃ J step KN (c) | J q KB ( c⇧ .n, c⇧ .l, c⇧ .l )}
N4 J step± [qp] KN (c) = {c⇧ ⌃ J step± KN (c) | C = J step± KN (c)⌦
J REWRITE± (qp,C, c⇧ ) KB ( c⇧ .n, c⇧ .l, c⇧ .l )}
N5 J {action /} KN (c.n) = { n⇧ , c.p, c.l } with n⇧ such that Raction (c.n, n⇧ )
N6 J {action} KN (c) = J AFP(action, c.n) KN (J {action /} KN (c))
N7 J step : M[= v] KN (c) = { c⇧ .n, c⇧ .p, OUT(c⇧ .n, M) | c⇧ ⌃ J step KN (c)}
N8 J (path) KN (c) = {cr | r ⌅ 0 ⌥0 ⇤ s ⇤ r :
cs+1 ⌃ J path KN (cs ) ⌦ c0 = c}
N9 J (path) {v, w} KN (c) = {cr | v ⇤ r ⇤ w ⌥0 ⇤ s ⇤ r :
cs+1 ⌃ J path KN (cs ) ⌦ c0 = c}
N10 J (expr)[qp] KN (c) = {c⇧ | c⇧ ⌃ C ⌦C = J expr KN (c)⌦
J REWRITE+ (qp,C, c⇧ ) KB ( c⇧ .n, c⇧ .l, c⇧ .l )}
N11 J doc(uri) KN (c) = Fdoc (uri)
26](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-26-320.jpg)
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![100,000+ pages, millions of results
#pages [1000] / #results [100,000]
200 160
memory
extracted matches 140
150 visited pages 120
memory [MB]
100
100 80
60
50 40
20
0 0
0 2 4 6 8 10 12
Constant Memory
(b) Millions of results
time [h]
32](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-32-320.jpg)
![700
time w/o page loading [sec]
OXPath
600 Web Content Extractor
Lixto
500 Visual Web Ripper
Web Harvest
Chickenfoot
400
300
200
100
0
0 20
faster
40 60 80 100 120 140
#pages 34](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-34-320.jpg)
![1600
time w/o page loading [sec]
1400 OXPath
Lixto
1200 Web Harvest
Chickenfoot
1000
800
600
400
200
0
even faster
0 100 200 300 400 500 600 700 800
Number of pages 35](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-35-320.jpg)
![350 OXPath
Lixto
300 Web Harvest
Chickenfoot
memory [MB]
250
200
150
only hundreds of pages as
100 tools fail for more pages
other
50
0
memory
0 100 200 300 400 500 600 700 800
#pages 36](https://image.slidesharecdn.com/oxpath-vldb-110914042517-phpapp02/85/Oxpath-vldb-36-320.jpg)
Oxpath vldb
- 1. DIADEM domain-centric intelligent automated data extraction methodology OXPath Scalable, Memory-efficient Data Extraction from Web Applications Andrew Sellers September 1st, 2011 @ Department of Computer Science, Oxford University joint work with Tim Furche, Georg Gottlob, Giovanni Grasso, Christian Schallhart
- 2. 1 A Lingua Franca for Web Extraction 2
- 3. 3
- 4. Seattle 4
- 5. 5
- 6. 6
- 7. 7
- 8. OXPath » Lingua Franca for Web Extraction 1 A Call for Action in Web Extraction! Past: Form Filling + HTML Patterns Now: Interaction + DOM Patterns getting to the data requires interaction not just form filling identifying relevant data from rendered DOMs including computed style and geometric information access to all CSS properties, but less rich relations than in SXPath 8
- 9. The nesting in the result mirrors the structure of the OX pression: extraction markers in a predicate (title, source sent attributes to the last marker outside the predicate (sto Kleene Star. Finally, we add the Kleene star, as in [1 example, the following expression queries Google for “O Seattle traverses all accessible result pages and extracts all links. doc("google.com")/descendant::field()[1]/{"Oxford"} /following::field()[1]/{click /} /( /descendant::a:<Link=(@href)>[.#="Next"]/{cli To limit the range of the Kleene star, one can specify up lower bounds on the multiplicity, e.g., (...)*{3,8}. doc("zillow.com")/descendant::field()[1]/{"Seattle"}/fo /descendant::input[@type=’checkbox’][2]/{uncheck}/follo //div[.="Beds"]/following-sibling::select/{"3+"/}//a[./ 9
- 10. The nesting in the result mirrors the structure of the OXPath ex- pression: extraction markers in a predicate (title, source) repre- sent attributes to the last marker outside the predicate (story). Kleene Star. Finally, we add the Kleene star, as in [12]. For example, the following expression queries Google for “Oxford”, traverses all accessible result pages and extracts all links. doc("google.com")/descendant::field()[1]/{"Oxford"} /following::field()[1]/{click /} /( /descendant::a:<Link=(@href)>[.#="Next"]/{click /} )* To limit the range of the Kleene star, one can specify upper and lower bounds on the multiplicity, e.g., (...)*{3,8}. doc("zillow.com")/descendant::field()[1]/{"Seattle"}/following::*#GOButton/{ /descendant::input[@type=’checkbox’][2]/{uncheck}/following::field()[1]/{unc //div[.="Beds"]/following-sibling::select/{"3+"/}//a[./text()="More filters" //input[following-sibling[contains(.,"Multi Family")]]/{uncheck/} /(//span.arrowNext/a/{click/})*//ul#search-results/li:<property> [//div.property-info//a/{click/}//div.home-description:<info=(.)> 10 z
- 11. OXPath » Lingua Franca for Web Extraction 1 Wrapper Babel Wrapper induction & data extraction systems each invent their own wrapper language often separate navigation and matching Main classes: (1) pattern matching + imperative navigation XPath Finite & Tree Automata Token Prefix/Suffix (2) Datalog E-Log (Lixto) 11
- 12. OXPath » Lingua Franca for Web Extraction 1 Why OXPath? scalability familiarity an XPath for simplicity data extraction web applications 12
- 13. 2 OXPath 13
- 14. Start at kayak.co.uk: doc("rightmove.co.uk") To select an airport, type a few letters and select from completion list //field().destination/{"Sea" /} //div#smartbox//li[1]/{click /} Submit the form 14
- 15. Refine the results by unchecking the “2+ stops”: //*#stops2/{uncheck } On all result pagesattributes Extract the /(//a[.=‘Next’]/{click /})* warnings Mouseover the ! to extract flight quality and//span.qualityWarningIcon/{mouseover /} for each flight //body.resultrow:<flight> Click on the details to extract layovers 15
- 16. 2 OXPath » The Language Interactive Wrapper for Kayak doc(‘‘kayak.co.uk’’)//input#origin/{“Lon” /} //div#smartbox//li[1]/{click /} //input#destination/{“Sea” /} //div#smartbox//li[1]/{click /} /descendant::field()[last()]/{click /} //*#stops1/{uncheck }/following::*#stops2/{click /} /(//a[.=’Next’])* //body.resultrow:<flight> [.//a.results_price:<price=string(.)>] [.//span.qualityWarningIcon/{mouseover /} //div.airqualitylist//tr:<warning=string(.)>] [.//a.resultdetaillink/{click /} //*.layover//td.airportCode:<layover=string(.)>]16
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- 18. 2 OXPath » The Language ➊ Actions: Browser Interaction Actions correspond to DOM events, e.g., Document doc("rightmove.co.uk") Click {click} Fill {“Sea”} Mouseover {mouseover} Executed once on each context node Return context nodes (contextual actions) or root nodes for new DOM (absolute actions) 18
- 19. 2 OXPath » The Language ➋ Extraction: Compact Tree Construction Extraction marker select nodes for extraction record markers: :<flight> attribute markers: :<price=string(.)> Extracted data has tree shape nesting of extraction markers in OXPath expression defines nesting of records and attribute-record associations in the output 19
- 20. 2 OXPath » The Language ➌ Iteration: Kleene Star Most web sites use pagination for results traversing paginated results require iteration ⇢ extraction from any unbounded component of a link graph Kleene Star from Regular XPath [Marx TODS ‘05] extended to OXPath, i.e., with action in the iterated expression /(//a[.=’Next’])* OXPath’s Page-at-a-time algorithm buffers in practice only a constant number of pages even for very large components 20
- 21. 2 OXPath » The Language ➋ Style: Querying Visual Attributes Access to all CSS properties via style axis Visibility style::display or style::visibility Font size style::font-size Geometry style::top, style::left, ... Color style::color or style::background-color Joins on style properties possible but: no rich spatial relations as in SXPath 21
- 22. 2 OXPath » The Language OXPath = XPath + 4 action extraction style iteration 22
- 23. 3 Analysis 23
- 24. OXPath » Formal Properties 3 Semantics – Overview Semantics defined over relational structure as in XPath Leashed [Benedikt 08] but: extended to multiple documents and with action relations action relations form tree ⇢ no two actions lead to same DOM but: instead of single node set, set of relations for extracted tree Context extended by last match for parent extraction marker necessary to construct the extraction tree last match for sibling extraction used for compact specification of records with mixed attributes and nested records 24
- 25. results … … 25
- 26. N1 J estep/path KN (c) = {c⇧⇧ | c⇧ ⌃ J estep KN (c) ⌦ c⇧⇧ ⌃ J path KN (c⇧ )} N2 J axis::nodes KN (c) = { n⇧ , c.p, c.l | Raxis (c.n, n⇧ ) ⌦ n⇧ ⌃ Rnodes } N3 J step[q] KN (c) = {c⇧ ⌃ J step KN (c) | J q KB ( c⇧ .n, c⇧ .l, c⇧ .l )} N4 J step± [qp] KN (c) = {c⇧ ⌃ J step± KN (c) | C = J step± KN (c)⌦ J REWRITE± (qp,C, c⇧ ) KB ( c⇧ .n, c⇧ .l, c⇧ .l )} N5 J {action /} KN (c.n) = { n⇧ , c.p, c.l } with n⇧ such that Raction (c.n, n⇧ ) N6 J {action} KN (c) = J AFP(action, c.n) KN (J {action /} KN (c)) N7 J step : M[= v] KN (c) = { c⇧ .n, c⇧ .p, OUT(c⇧ .n, M) | c⇧ ⌃ J step KN (c)} N8 J (path) KN (c) = {cr | r ⌅ 0 ⌥0 ⇤ s ⇤ r : cs+1 ⌃ J path KN (cs ) ⌦ c0 = c} N9 J (path) {v, w} KN (c) = {cr | v ⇤ r ⇤ w ⌥0 ⇤ s ⇤ r : cs+1 ⌃ J path KN (cs ) ⌦ c0 = c} N10 J (expr)[qp] KN (c) = {c⇧ | c⇧ ⌃ C ⌦C = J expr KN (c)⌦ J REWRITE+ (qp,C, c⇧ ) KB ( c⇧ .n, c⇧ .l, c⇧ .l )} N11 J doc(uri) KN (c) = Fdoc (uri) 26
- 27. OXPath » Formal Properties 3 Page-At-A-Time (PAAT) Assures constant memory over number of pages traversed Experimentally confirmed small overhead over XPath overhead due to nested record extraction actions do not affect complexity Kleene star: small overhead over regular XPath Extracted records are never buffered but streamed as soon as they are matched Offers optimal page management by minimising buffer size 27
- 28. Web Images Videos Maps News Shopping Gmail more ! 1 world wide web Web Images Videos Maps News Shopping Gmail more ! 2 Web Images Videos Scholar Articles and patents world wide web Maps Newsanytime Shopping Gmail more include cit 1 3 Web Images patents The Scholar of Articles and Videos Maps world wide web diameter the world wide web Newsanytime Shopping Gmail m inclu R Albert, H Jeong, AL Barabási - Arxiv preprint cond-mat/9907038, 1999 arXiv:cond-mat/9907038v2 [cond-mat.dis-nn] 10 Sep 1999 The diameter Despite itsScholar role in communication,web The diameter of Articles and patents the world wide web (www) the world wide world wide increasing web anytime R Albert, H Jeong,individual or institution can create websites with u controlled medium: any AL Barabási - Arxiv preprint cond-mat/9907038, Cited arXiv:cond-mat/9907038v2 -[cond-mat.dis-nn]web versions by 2497 - diameter of theView as HTML - All 52 1999 The diam Related articles 10 Sep The Scholar role in communication, the world wide web ( world wide Despite its increasing Articles and patents anytime R Albert, H Jeong, AL Barabási - Arxiv preprint cond-mat/9907 controlled medium: any individual or institution can create websites Self-similarity in World Wide Web traffic: evidence and poss CitedarXiv:cond-mat/9907038v2 - View as HTML - 10 Sep 1999 The by 2497 - Related articles [cond-mat.dis-nn] All 52 versions ME Crovella, A The diameter of the communication,webworld wide w Despite its increasing role in world wide 2002 - ieeexplore Bestavros - Networking, IEEE/ACM ", the 1 2 7 1 12 Abstract—Recently, the notionanyself-similarity institution can create webs controlled medium: of individual or has been shown to apply Self-similarity in HIn this paper, we[cond-mat.dis-nn] 10cond-mat R Albert, Jeong, AL Barabási - Arxiv preprint network traffic.-World Wide Web traffic: evidence and local-area CitedarXiv:cond-mat/9907038v2 -show evidence that the subse by 2497 Related articles View as HTML - All Sepversi 52 199 is due to WorldDespiteWeb (WWW) transfers IEEE/ACMcharacteristics th ME Crovella, A Bestavros - Networking, can show ", 2002 - ieeex Wide its increasing role in communication, the world w Cited Abstract—Recently,articles - BLof self-similarityversions evidence a by 3122 -controlled the notion Direct - All 56 institution can create Related medium: any Wide Web has been shown to individual or traffic: Self-similarity in Worldpaper, we show evidence that the local-area Cited by 2497 - In this articles - View as HTML - All 52 network traffic. 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This universe Cited by 3122 - Related articlesB " - Internet ", 2010 - - BL 7 T Berners-Lee, R Cailliau, JF Groff, the aims, data model, and protocols needed to implement the “web [BOOK] Information architecture forWeb (W 3 ) initiativewebpractica the world wide is a CitedPurpose – Related articles - Check Availability - BL Direct - All by 1919 - The World-Wide L Rosenfeld, P World-wide web: The information universe information universe - portal.acm.org Morville - 1998 into existence using available technology. Information Architecture for the R and protocols needed to- implement the the aims, data model,World Wide Web isB "webmasters, des for Internet ", 20 Information site. It's for novice Groff, 3 ) initiative webpra T Berners-Lee, Cailliau, JF involved inCitedPurpose – The World-Wide Checkworld wideBLfrom t [BOOK]building a web architecture for the designers who, 2 web(W 12 by 1919 - Related articles - Web Availability - is Direc L Rosenfeld, P Morville designed sites. 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- 29. OXPath » Formal Properties 3 Summary of Complexity Combined: PTIME-hard PTIME-hard Data: NLOGSPACE LOGSPACE Extraction marker = n-ary, nested queries Time Space OXPath w/o Actions & Kleene Actions = multiple pages O( n6⋅q2 ) O(n4⋅q2) O( n5⋅q2 ) O(n3⋅q2) OXPath w/o Kleene O( (p⋅n)6⋅q3 ) O( n5⋅q3 ) OXPath w/o unbounded Kleene O( (p⋅n)6⋅q3 ) Contextual actionsO( n5⋅q∑3 ) prefix) (action free OXPath (full) O( (p⋅n)6⋅q3 ) O( n5⋅(q+d)3 ) Buffer bounded by page depth 29
- 30. OXPath » Formal Properties 3 Page-At-A-Time (PAAT) node-set semantics extraction semantics complexity close to XPath parallelizable 30
- 31. 4 Evaluation 31
- 32. 100,000+ pages, millions of results #pages [1000] / #results [100,000] 200 160 memory extracted matches 140 150 visited pages 120 memory [MB] 100 100 80 60 50 40 20 0 0 0 2 4 6 8 10 12 Constant Memory (b) Millions of results time [h] 32
- 33. PAAT browser initialization page rendering 2% 13% 2% 13% 85% browser bound 33
- 34. 700 time w/o page loading [sec] OXPath 600 Web Content Extractor Lixto 500 Visual Web Ripper Web Harvest Chickenfoot 400 300 200 100 0 0 20 faster 40 60 80 100 120 140 #pages 34
- 35. 1600 time w/o page loading [sec] 1400 OXPath Lixto 1200 Web Harvest Chickenfoot 1000 800 600 400 200 0 even faster 0 100 200 300 400 500 600 700 800 Number of pages 35
- 36. 350 OXPath Lixto 300 Web Harvest Chickenfoot memory [MB] 250 200 150 only hundreds of pages as 100 tools fail for more pages other 50 0 memory 0 100 200 300 400 500 600 700 800 #pages 36
- 37. OXPath » System & Evaluation 3 Minimal constant memory minimal page buffer browser bound very low overhead 37
- 38. 4 OXPath Suite 38
- 39. generalized to create a list of similar elements. An add OXPath » OXPath Suite Interface – Before Expression Refinement Figure 3.6: User 4 how many nodes this expression extracts. Clicking on alternatively in ascending and descending order. Visual OXPath: Semi-supervised Generation Interaction recording Generation of OXPath expressions ranked by robustness & specificity Figure 3.4: User Interface – Action Prope Users can select another expression in the list th suitable. They can also adapt the generated OXPa expression manually. For assistance, the syntactic corre and the number of nodes it selects is updated durin 39
- 40. 4 OXPath » OXPath Suite OXPath Tracer: Debugging Track selected DOM nodes Trace page management Fine grained execution control (filter, step-by-step, breaks) 40
- 41. 4 OXPath » OXPath Suite ONTOX: Ontology Population with OXPath 41
- 42. DIADEM domain-centric intelligent automated data extraction methodology
- 43. DIADEM domain-centric intelligent automated data extraction methodology Questions diadem-project.info