XML to XML through XML

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XML to XML through XML

• Pim Lemmens
• Geert-Jan Houben

Eindhoven University of Technology Dept. of
Computer Science
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XML to XML through XML

• How Adaptation of XML Transformations May Be Done
  by the Same Tool As Used for the Transformations
  Themselves

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Hera Architecture
Relational Database
Object-Oriented Database
XML Database

ODB-XML Wrapper
RDB-XML Wrapper
Mediator/ Integrator
Information Retrieval
User/Platform Adaptation
Hypermedia Presentation
Logical Presentation
Logical-WML Presentation
Logical-SMIL Presentation
Logical-HTML Presentation
HTML Presentation
SMIL Presentation
WML Presentation
Query

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XML Transformations

• Document screening
• Data retrieval, querying
• Applying style sheets
• Adaptation of those transformations to
• User profiles
• Platform requirements
• Producer preferences
• ..

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Transformations in HERA
Source data
Query adaptation
Generic query
Adapted query
Filtered data
Generic stylesheet
Adapted stylesheet
Output data
Stylesheet adaptation
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Transformation Tools

• XSLT
• XQuery
• Something different (for adaptation) HTL

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Single Tool for All Transformations

• transformation of documents
• transformation of transformation specifications
• transformation specifications documents
• transformation specification schema
• document instance
• schema instance

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Transformation and Document

• House query (schema)
• lthousegt
• ltpricegt
• 120,000
• lt/pricegt
• lt/housegt

• House doc (instance)
• lthouse idh123gt
• ltpricegt
• 100,000
• lt/pricegt
• ltaddressgt..lt/addressgt
• lt/housegt
• lthouse idh234gt

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Requirements for HERA Transformations

• Isomorphism between schema and instance
• Separate items separately accessible
• Separation of input and output document
  specifications
• One uniform mechanism for specifying structure,
  values and operations, independent of their use

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Req 1 Isomorphism Schema - Instance

• Schema element/attribute name instance
  element/attribute name
• Schema children or attributes of element ?
  instance children or attributes of element
• Schema element/attribute values ? instance
  element/attribute values
• Arbitrary length list in instance represented by
  e.g. special kind of loop in schema

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Req 2 Separate Items Separately Accessible

• All HTL entities should be accessible to HTL
• Items to be found in input
• Values to be changed
• Items to be used for output
• Operands to be used in calculations
• DOM nodes
• Elements
• Attributes
• Text nodes

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DOM Nodes
house

• lthouse year1980gt
• ltpricegt
• 120,000
• lt/pricegt
• Nice house in
• good condition
• lt/housegt

year
price
Nice ..
120,000
1980
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Req 3 Separation of Input Output Spec

• Output spec not limited by input spec
  requirements
• Input spec not limited by output spec
  requirements
• Requires links between input and output spec
• Output and input spec may use same formalism

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Req 4 One Mechanism for All

• Output specification (structure, values, names)
• Input selection (structures, values, names)
• Calculation (operators, operands)
• All described using templates

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Input and Output Templates

• Input template
• lthtltemplategt
• lthouse htlid123gt
• ltprice/gt
• ltaddress/gt
• ltcity/gt
• lt/housegt
• lt/htltemplategt

• Output template
• lthtltemplategt
• lthtlselect idref123gt
• ltexpensesgt
• lthtlvalue-ofgt
• ltprice/gt
• lt/htlvalue-ofgt
• lt/expensesgt

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Requirements for HERA Transformations

• Recap
• Isomorphism between schema and instance
• Separate items separately accessible
• Separation of input and output document
  specifications
• One mechanism for specifying structure, values
  and operations

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Why Not Use XSLT?

• Well tested, efficient and widely available
• Structure of specification very different from
  structure of documents
• Paths defined using XPath expressions hard to
  transform
• Input driven processing (and output) order
  determined by input document.

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Why Not Use XQuery?

• Separate query and output generation parts
• Output spec has XML structure
• But, input spec has not an XML structure query
  part needs string parsing

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HTL HERA Transformation Language

• Templates used for input spec, output spec and
  calculation spec
• Separate output spec input spec templates
• Templates may use sub-templates
• Filter specification input data to be used
• Selection specification retrieved data to be
  inserted in output or used for calculations

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Templates and Sub-templates

• ltagt
• ltbgt .. lt/bgt
• ltcgt lthtlparam idrefp/gt lt/cgt
• ltd/gt
• lt/agt
• lthtltemplate htlidpgt ltqgt ltrgt lt/htltemplategt

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Filtering and Selection
Filter specification
Output specification
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Templates and Path Expressions

• lthtltemplategt
• ltagt
• ltb htlidxyzgt
• ltd/gt lte/gt ltf/gt
• lt/bgt
• lt/agt
• lt/htltemplategt

• Equivalent XPath expression when accessed through
  idref xyz
• a/bd e f

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Templates and Calculations

• lthtlattribute nameagt
• lthtlfromgt
• lthtloperator opgt
• ltprice/gt
• 10
• lt/htloperatorgt
• lt/htlfromgt
• lt/htlattributegt

• XPath
• _at_a gt (price 10)

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List of HTL Elements

• htltransform
• htltemplate
• htloutput
• htlattribute
• htlfrom
• htlto
• htloperator
• htlparam

• htlany
• htl descendant
• htlselect
• htlname-of
• htlvalue-of
• htlcopy
• (attribute) htlid

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Implementation

• XSLT
• Proven technology
• HTL-to-XSLT conversion by XSLT
• Semantics defined in terms of XSLT
• Use of XPath operators
• Additional translation step required
• Use of separate XSLT templates and modes not
  possible

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Conclusions

• Tool for XML transformations that allows
  transformations on transformations
• Schema isomorphic to instance
• Basic entities correspond to DOM nodes
• Separation of input output specification
• All expressions represented by XML structures
• Implementation XSLT

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Contact Information

• W.J.M. Lemmens
• Eindhoven University of Technology
• P.O. Box 513
• NL 5600 MB Eindhoven
• E-mail W.J.M.Lemmens_at_tue.nl
• Phone [phone]

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