WebOQL: Restructuring Documents, Databases and Webs

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WebOQL Restructuring Documents, Databases and
Webs

• Gustavo O. Aracena
• Alberto O. Mendelzon

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Background

• Background
• widespread use of Web
• new data management problems
• What is WebOQL?
• combination of architecture, data model and query
  language on which we would be able to extract
  information from online structured documents
  effectively withouth custom-tailored programs

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Data Model

• Tree-based data model
• hypertree ordered arc-labeled trees
• arcs internal and external
• internal arcs are used to represent structured
  objects
• external arcs are used to represent references
  among object
• external arcs cannot have descendants
• external arcs must have a field named Url
• Hypertrees are useful because they subsume three
  abstractions collections, nesting, and ordering

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Data Model

• Web
• a pair(t, F) consisting hypertree t and a
  function F that maps URLs to hypertrees
• t is the schema
• F is the browsing function of the web
• Tails
• Tails of trees of t obtained by chopping off
  prefixes of t
• Simple trees
• Simple trees of t are the trees composed of one
  arc followed by a tree that stems from ts root
• Subtrees
• subtrees of tree t are the trees at the end of
  the arcs that stem from ts root

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Data Model

• Operators
• Prime operator () returns the first subtree of
  its argument
• Peek operator (.) extracts a field from the
  record that labels the first outgoing arcs of its
  argument
• Hang operator () builds an arc labeled with a
  record formed with the arguments
• Tilda () is used for string matching pattern
• Concatenate () to juxtapose two trees
• Head ( n) returns the first n simple trees of a
  tree (n gt0)
• Tail (!) returns all but the first simple tree of
  a tree

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Operators
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Query

• Input of query in WebOQL URL deferencing
• URL deferencing means replacing URL with the
  result of applyting the browsing function of the
  current web to it
• Web restructuring query
• a function that maps a web into another
• example
• this select y.Title, y.Url as schema
• from x in csPapers, y in x
• where y.Authors Smith
• generalization
• select q1 as s1, q2 as s2, , qm as sm
• qi are queries
• si is either a string query or the keyword schema

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Restructuring Web
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Structured Documents

• Structured documents modeled as abstract syntax
  trees (AST)
• Each arc in AST corresponds either to a
  subdocument enclosed in an occurrence of a paired
  tag, to a nonpaired tag, or to a piece on an
  untagged text

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Restructuring Documents

• Navigational patterns
• regular expressions over an alphabet of record
  predicates
• Tail variables
• iterate over tails, instead of simple trees
• indicated by capital letter
• example
• Tag OL /
• select Tag LI / X3
• from X in browse(Card Punching.html)!
• where X.Tag H3