Translating XQuery into XSLT

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Translating XQuery into XSLT

• Stephan Lechner, Günter Preuner, Michael Schrefl
• Johannes Kepler University of Linz
• Homepage http//www.dke.uni-linz.ac.at

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Contents

• Introduction
• XQuery to XSLT Differences to bridge
• Translation and Transformation
• XQ2XSL-Translator
• Conclusion

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1. Introduction

• XSLT
• Transformations and presentational markup
• Adopted by industry (e.g. in Web-Browsers)
• Most beneficial Client Side Processing
• XQuery
• Typed query language for XML documents
• Most beneficial Server Side Processing
• Comfortable to use

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Scenario Different Views of Data
Authors and Books (XML)
Authors View (XSL)
Books View (XSL)
Client Side
Server Side
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Views using XQuery and XQ2XSL
Authors View Transfor- mations (XQuery)
Templates For Presentation (XSL)
Authors View Presentation (XSL)
Authors View Transfor- mations (XSL)
XQ2XSL
Combine
Authors and Books (XML)
Authors View (XSL)
works on
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Motivation

• Expressing complex transformations for views
  conveniently using XQueries
• Perform these transformations on Client Side
  using XSLT only (yet implemented by many
  browsers)

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2. XQuery to XSLT Differences

• Different data models
• Node identity
• Interim query results
• Different language constructs
• Closure
• Parameter binding byposition vs. name
• Nested variables scopes

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Bridging Data Model Differences

• To avoid case-distinctions, we use an Internal
  Data Model with...
• Explicit Node Identifiers
• Wrapper elements around attributes, PIs, comments

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Language Construct Differences

• FOR b
• IN annualBooks(2001)
• RETURN
• LET b b/title
• RETURN b

• ltvariable name"FOR1_outer"gt
• ltcall-template name"annualBooks"gt
• ltwith-param name"yearParam"
• select"2001"/gt
• lt/gtlt/gt
• ltfor-each select"FOR1_outer/"gt
• ltvariable name"FOR1 select"."/gt
• ltvariable name"LET1"gt
• ltcopy-of select"FOR1/title"/gt
• lt/gt
• ltcopy-of select"LET1"/gt
• lt/gt

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3. Translation and Transformation
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4. XQ2XSL Translator

• Parse tree generation and augmentation
• Names of auxiliary variables
• Aliases for XQuery-variables
• Determine parameter names and positions
• Node Translation
• Traverse the parse tree (depth first)
• Translate each node

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Parse Tree Generation Augmentation
LET b b/title RETURN b
letexp LET Variablevar EQUAL
Exprouter RETURN Exprinner
Alias(b)Let1
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FOR b IN annualBooks(2001) RETURN LET b
b/title RETURN b
Param- pos1
Var
b
Proj
Var
Alias(b) Let1
b
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Implementation CUP Parser Generator
Grammar (production)

• letexp LET Variablevar
• EQUAL Exprouter
• RETURN Exprinner
• Node n new LetExpressionNode ()
• n.setChild ("Variable", var)
• n.setChild ("OuterExpression", outer)
• n.setChild ("InnerExpression", inner)
• var.setParent (n)
• outer.setParent (n)
• inner.setParent (n)
• inner.setAlias (var.getLiteralValue(),
• Node.newAlias())
• RESULT n

Parse Tree Generation and Augmentation using Seman
tic Actions
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Parse Tree Traversal Node Translation
AN
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Node Translation by Transition Rules
IF (Type(AN) LetExpression) THEN NV(AN)
ltvariable name1"gt2lt/gt3
1 Alias (Child (inner), LitValue
(Child (var)) 2 NV (Child (outer)) 3 NV
(Child (inner))
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Implementation Node Translation (Java)

• class LetExpressionNode extends Node
• void translate ()
• // Depth-first traversal
• getChild (var").translate ()
• ... translate the other children
• // get values for the place holders
• String alias getChild(inner).
• getAlias (getChild
  (var).getLiteralValue())
• ... values of the other place holders
• // Evaluate the value of "self"
• setNodeValue ("ltxslvariable name\""
• alias ... )

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5. Conclusion

• Advantages of XQuery High-level query language
  with type-checking
• Advantages of XSLT well suited for
  presentational markup, widely distributed and
  adopted by industry
• Translating XQuery into XSLT complex
  transformations can be expressed in XQuery and
  performed as XSLT.

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Future Work

• Automatic splitting of XQueries into server-side
  and client-side parts
• Parameterizing XQueries for personalization
  purpose
• Extending the concept by runtime type information
  

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(a) Views Data defined by XQueries
Authors and Books (XML)
Authors View Transfor- mations (XQuery)
Templates For Presentation (XSL)
Authors View Presentation (XSL)
XQuery
Combine
Authors View (XSL)
Authors View Data (XML)
works on