Intelligent Querying of Web Documents Using a Deductive XML Repository

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Intelligent Querying of Web Documents Using a
Deductive XML Repository

• Nick Bassiliades, Ioannis Vlahavas
• Dept. of Informatics
• Aristotle University of Thessaloniki

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Abstract

• X-DEVICE is a deductive OODB system
• It is used for storing XML documents as objects
• X-DEVICE has a powerful rule-based query language
  for
• intelligently querying stored XML documents
• publishing the results
• The rule language features
• second-order syntax
• generalized path and ordering expressions
• Metadata are used to translate the extended
  features into first-order rules

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Object Model of XML Data

• DTD definitions are automatically translated into
  a class schema
• XML documents are automatically translated into
  objects
• Generated classes and objects are stored within
  the underlying OODB ADAM
• ADAM is an OODB built on Prolog (Norman Paton,
  Peter M.D. Gray, Univ. of Aberdeen)

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Object Model of XML DataW3C XQuery TEXT Use Case

• lt!ELEMENT company (name, ticker_symbol?,
  description?, business_code, partners?,
  competitors?)gt
• lt!ELEMENT name (PCDATA)gt
• lt!ELEMENT ticker_symbol (PCDATA)gt
• lt!ELEMENT description (PCDATA)gt
• lt!ELEMENT business_code (PCDATA)gt
• lt!ELEMENT partners (partner)gt
• lt!ELEMENT partner (PCDATA)gt
• lt!ELEMENT competitors (competitor)gt
• lt!ELEMENT competitor (PCDATA)gt

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Object Model of XML DataAlternation

• lt!ELEMENT content (par figure) gt

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Deductive XML Query Language

• The X-DEVICE language is an extension of DEVICE,
  the basic deductive rule language
• N. Bassiliades, I. Vlahavas, A.K. Elmagarmid,
  E-DEVICE An extensible active knowledge base
  system with multiple rule type support, IEEE
  TKDE, 12(5), 824-844, 2000.
• X-DEVICE rules are pre-compiled into DEVICE
  deductive rules
• Deductive rules are compiled into production
  rules
• ECA rules with one complex event
• Matching through RETE network

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X-DEVICE LanguageBasic first-order deductive
rules

• if C_at_company(nameXYZ Ltd,
• partner.partners ? P)
• then partner_of_xyz(partnerP)
• Selects company C with name XYZ Ltd
• Iterates over partners P through navigation
• Path inverse notation NOT partners.partner
• Defines a new derived class of partners of
  company XYZ
• Derived objects are materialized

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X-DEVICE Language Recursion

• if P_at_partner_of_xyz(partnerP1)and
• C_at_company(nameP1,
• partner.partners ? P2)
• then partner_of_xyz(partnerP2)
• Rule processing uses semi-naïve evaluation
• Negation is allowed (safety, stratification)
• Single-valued attributes use for instantiation
• Multi-valued attributes use ? for instantiation
• Prolog lists guarantee correct ordering

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X-DEVICE LanguageVariable-Attribute Expressions

• if C_at_company(A XYZ)
• then a_xyz_comp(companylist(C))
• We dont know which attribute of company contains
  the string XYZ
• A is second-order variable (meta-variable)
• list is an aggregation function (collects company
  OIDs in a multi-valued attribute)
• The operator performs string search

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X-DEVICE LanguageTranslation of
Variable-Attributes

• if company_at_xml_seq(elem_order ? A)
• then new_rule(
• if C_at_company(A XYZ)
• then a_xyz_comp(companylist(C))
• ) gt deductive_rule
• Iterate over meta-class xml_seq to find all
  attributes (sub-elements) of class company
• A production rule creates one deductive rule for
  each instantiation of A
• A is now a first-order variable in the condition
  and a constant in the action

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X-DEVICE LanguageGeneralized Path Expressions

• if C_at_company( XYZ)
• then a_xyz_comp(companylist(C))
• The search for string XYZ must be performed
• not only to attributes of company
• but also to attributes of objects contained
  within company
• at all levels of nesting

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X-DEVICE LanguageTranslation of Generalized Paths

• Iterate over all immediate elements of class
  company
• Store them into an auxiliary derived class
• if company_at_xml_seq(elem_order ? X1)
• then tmp_elem1(cnd_elemX1,
• pathX1)

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X-DEVICE LanguageTranslation of Generalized Paths

• Recursively iterate over all elements and
  sub-elements stored in the auxiliary class
• The path-so-far from the root company element is
  accumulated
• if X1_at_tmp_elem1(cnd_elemX2,pathX3)
• and X2_at_xml_seq(elem_order ? X4)
• then tmp_elem1(cnd_elemX4,
• pathX4X3)

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X-DEVICE LanguageTranslation of Generalized Paths

• Terminate the recursion if no more nested
  elements can be found
• Create one deductive rule for each discovered
  concrete path
• if X1_at_tmp_elem1(cnd_elemX2,pathX3) and
• not X2_at_xml_seq and
• prologcreate_path(X3,PATH)
• then new_rule(
• if C_at_company(PATH XYZ)
• then a_xyz_comp(companylist(C))
• ') gt deductive_rule

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X-DEVICE LanguageTranslation of Generalized Paths

• The following deductive rules are created
• C_at_company(name XYZ)
• C_at_company(ticker_symbol XYZ)
• C_at_company(description XYZ)
• C_at_company(business_code XYZ)
• C_at_company(partner.partners XYZ)
• C_at_company(competitor.competitors XYZ)
• Optimization of multiple rules is achieved
  through common parts of the RETE network
• The DEVICE system takes care of that

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X-DEVICE LanguageOrdering Expressions

• W3C TEXT Case Query 5
• For each news item that is relevant to the
  Gorilla Corp, create an item summary element.
• The content of the item summary is the content of
  the title, date, and first paragraph of the news
  item
• if N_at_news_item(.contentGorilla Corp,
  par.content ?1 PAR,
• titleT, dateD)
• then item_summary(titleT,dateD,
• parPAR)

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X-DEVICE LanguageTranslation of Ordering

• Collect all the paragraphs that satisfy the
  condition
• Store them in a list of an auxiliary derived
  class
• if N_at_news_item(.contentGorilla Corp,
  par.content ? X1,
• titleT, dateD)
• then tmp_elem1(tmp_var1T, tmp_var2D,
• tmp_objlist(X1))

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X-DEVICE LanguageTranslation of Ordering

• Isolate a sub-list of all the paragraphs that
  satisfy the ordering expression ?1
• There is one Prolog goal for each ordering
  expression
• if X3_at_tmp_elem1(tmp_var1T,tmp_var2D,
• tmp_objX1) and
• prologlength(X2,1),append(X2,_,X1)
• then tmp_elem2(tmp_var1T,tmp_var2D,
• tmp_objX2)

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X-DEVICE LanguageTranslation of Ordering

• Iterate over all qualifying results and return
  them into the target element
• if X1_at_tmp_elem2(tmp_var1T,tmp_var2D,
• tmp_obj ? PAR)
• then item_summary(titleT,dateD,
• parPAR)

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X-DEVICE LanguageBuilding Result Documents

• The top-level element of the XML result document
  is identified with the keyword xml_result
• The DTD of the result document is identified
  through object references
• W3C TEXT Case Query 2
• Find news items where the Foo Corp company and
  one or more of its partners are mentioned in the
  same paragraph and/or title
• List each news item by its title and date

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X-DEVICE LanguageBuilding Result Documents

• Find the Foo company and iterate over its
  partners
• For each partner, iterate over news items and
  search for Foo and its partner inside the title
  of the same news item
• if C_at_company(nameFoo Corp,
• partner.partners ? P) and
• N_at_news_item(titleTFoo Corp P,
• dateD)
• then xml_result(news_item1(titleT,
• dateD))

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X-DEVICE LanguageBuilding Result Documents

• Find the Foo company and iterate over its
  partners
• For each partner, iterate over news items and
  search for Foo and its partner inside the
  nested paragraphs of the same item
• if C_at_company(nameFoo Corp,
• partner.partners ? P) and
• N_at_news_item(.par.contentFoo Corp
• P,
  titleT, dateD)
• then news_item1(titleT,dateD)

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X-DEVICE LanguageBuilding Result Documents

• lt!DOCTYPE news_item1
• lt!ELEMENT news_item1
• (title, date)gt
• lt!ELEMENT title (PCDATA)gt
• lt!ELEMENT date (PCDATA)gt
• gt
• The structure of the title and date elements is
  automatically determined by the type of the
  corresponding rule variables

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Advantages of X-DEVICE

• Logic-based query languages have
• well-understood mathematical properties
• declarative nature
• advanced optimization techniques (magic-sets)
• X-DEVICE compared to XQuery (functional)
• more high-level, declarative syntax
• more compact and comprehensible
• general path expressions
• due to fixpoint semantics and second-order
  variables

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Advantages of X-DEVICE

• Users can express complex XML document views
• Information customization for e-commerce,
  e-learning, etc.
• X-DEVICE offers multiple knowledge representation
  formalisms
• Deductive, Production, and Active rules
• Structured objects
• Production and Active rules can be used to update
  XML documents
• All the above can play an important role as an
  infrastructure for the Semantic Web

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Intelligent Querying of Web Documents Using a
Deductive XML Repository

• Nick Bassiliades, Ioannis Vlahavas
• Dept. of Informatics
• Aristotle University of Thessaloniki
• X-DEVICE site
• www.csd.auth.gr/lpis/systems/
• x-device.html