A Graphical Environment to Query XML Data with XQuery

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A Graphical Environment to Query XML Data with
XQuery

• campi_at_elet.polimi.it

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ltbibgt ltbook year"1994"gt lttitlegt
TCP/IP Illustrated lt/titlegt ltauthorgt
ltlastgt Stevens lt/lastgt
ltfirstgt W. lt/firstgt lt/authorgt
ltpublishergt Addison-Wesley lt/publishergt
ltpricegt 65.95 lt/pricegt lt/bookgt ltbook
year"1992"gt lttitlegt Advanced
Programming in the Unix...lt/titlegt
ltauthorgt ltlastgt Stevens lt/lastgt
ltfirstgt W. lt/firstgt lt/authorgt
ltpublishergt Addison-Wesley lt/publishergt
ltpricegt 78.99 lt/pricegt lt/bookgtlt/bibgt
XML data from the W3C Use Cases
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XQuery

• List books published by Addison-Wesley after
  1991, including
• their year and title
• ltbibgt
• for b in document("www.bn.com/bib.xml")/bib/boo
  k
• where b/publisher"Addison-Wesley" and
• b/_at_yeargt1991
• return ltbook year" b/_at_year "gt
• b/title
• lt/bookgt
• lt/bibgt

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XQBE (XQuery By Example)

• XQBE, a visual dialect of XQuery inspired by QBE
  paradigm (Zloof 77).
• The availability of simpler XQuery dialects
  could contribute to its success, especially for
  users with a very limited experience of query
  languages.
• To fit the XML data model, XQBE uses hierarchical
  structures to denote the data taken in input and
  generated as output. Such structures are
  annotated to express selection predicates, while
  explicit bindings visualize the input/output
  mappings.

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Motivation and design principles

• XQBE was designed with the objectives of being
• intuitive
• easy to map directly to XQuery
• capable of running on top of any existing XQuery
  engine
• XQBE includes most of the expressive power of
  XPath
• XQBE allows for arbitrarily deep nesting of
  XQuery FLWOR expressions
• XQBE supports the construction of new XML
  elements and permits to restructure existing
  documents

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Visual querying paradigm

• A vertical line divides the source (left) part
  from the construct (right) part.
• The query has a natural reading order from left
  to right.

Result data
Source data
Data Flow
Bindings

• The left part describes the data to be matched to
  construct the result, the right one specifies
  which parts will be retained in the result,
  together with (optional) newly generated items.

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XQBE
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• Element projection and renaming

For each book in the bibliography, list the title
and authors, grouped inside a result element
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Element projection and renaming
For each book list only the title and the
surnames of the authors
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Join between two documents
For each book found at both www.bn.com
and www.amazon.com, list the title of the book
and its price from each source
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Document restructuring
Create a flat list of all the title-author pairs,
with each pair enclosed in a result element
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Filtering nodes in the construct part
Make a list of all the books with their title,
including the editors only if they are affiliated
to CITI
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Sorting
List books published by Addison-Wesley after
1991, including their year and title, sorting the
retrieved books in lexicographic order
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Nesting and negation
List all the books not published by
Addison-Wesley and with an author whose first
name is Jack. Rename each of these books in
ltJack-s-bookgt, and only retain the title and the
full name of the authors whose first name is Jack
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Translation principles

• A query translates to one XQuery FLWR expression
• It can be contained into an arbitrary number of
  node constructors
• The for clause of the outmost FLWR expression
  contains a list of variable bindings, each of
  which corresponds to a binding edge
• Where clauses have a fixed structure
• existential quantifier (some...satisfies)

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The tool in action
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Future works

• Extend the set of supported core functions and
  add the capability of querying the document order
• Specialize XQBE with capabilities specific to
  some applicative domain
• An XQBE for digital libraries
• Produce the XQBE view of a given XQuery statement

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Conclusions

• XQBE is a graphical query language that offers a
  visual interface to query XML documents.
• We have presented a prototype that implements our
  proposed interface and translates graphical
  queries into XQuery, so that it can be used in
  conjunction with any XQuery engine.