1 Xslt Header Xslt Templates Xslt stylesheets MUST include this - - PDF document

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XSLT

Based on slides by Dan Suciu University of Washington

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Xpath: Summary

bib matches a bib element * matches any element / matches the root element /bib matches a bib element under root bib/paper matches a paper in bib bib//paper matches a paper in bib, at any depth //paper matches a paper at any depth paper|book matches a paper or a book @price matches a price attribute bib/book/@price matches price attribute in book, in bib bib/book/[@price<“55”]/author/lastname matches…

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Overview

Querying XML: XPath Transforming XML: XSLT

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Xslt – Transforming Xml

Amazon.com order form:

<single_book_order> <title>Databases</title> <qty>1</qty> </single_book_order>

Supplier’s order form:

<form7957> <purchase item=’book’ property=’title’ value=’Databases’ quantity=’1’/> </form7957>

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Xslt - Extensible Style Language for Transformation

Xslt is a language for transforming or

converting one Xml format into another Xml format.

Benefits:

• No need to parse or interpret many different Xml

formats – they can all be transformed to a single format to facilitate interpretation

• Language looks like Xml! (remember, Xml defines

languages!)

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Xslt – A First Look

< single_book_order> < title> Databases< /title> < qty> 1< /qty> < /single_book_order> < form7957> < purchase item= ’book’ property= ’title’ value= ’Databases’ quantity= ’1’/> < /form7957>

< ?xml version= '1.0'?> < xsl:stylesheet xmlns:xsl= 'http://www.w3.org/1999/XSL/Transform' version= '1.0'> < xsl:template match= 'single_book_order'> < form7957> < purchase item= 'book' property= 'title' value= '{ title} ‘ quantity= '{ qty} '/> < /form7957> < /xsl:template> < /xsl:stylesheet>

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Xslt – Header

Xslt stylesheets MUST include this body:

<?xml version='1.0'?> <xsl:stylesheet xmlns:xsl='http://www.w3.org/1999/XSL/Transform' version='1.0'> … </xsl:stylesheet>

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Xslt – Templates

Xslt stylesheets are a collection of templates

• Templates are like functions
• The body of a template is the output of a

transformation

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Xslt - Templates

You define a template with the

<xsl:template match=‘’> instruction

You call a template with the

<xsl:apply-templates select=‘’> instruction

• 1. All elements or attributes that satisfy the select attribute

expression are selected.

• 2. For each element or attribute that is selected:
• i. A matching template is found in the stylesheet.
• ii. The body of the template is executed.

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Xslt – Template Matching

Xml <basket> <apple color=‘red’/> <apple color=‘green/> <apple color=‘green/> <box> <orange taste=‘good’/> <peach/> <apple color=‘red’/> </box> </basket> Transformed Xml: <new_basket> <apple/> <apple/> <apple/> <box/><apple/> </new_basket> Stylesheet <xsl:template match=‘basket’> <new_basket> <xsl:apply-templates select=‘apple’/> <xsl:apply-templates select=‘box’/> </new_basket> </xsl:template> <xsl:template match=‘apple’> <apple/> </xsl:template> <xsl:template match=‘box’> <box/> <xsl:apply-templates/> <xsl:template> 11

Xslt – choose Instruction

<xsl:choose> instruction is similar to a C++ or

Java switch statement

<xsl:when test=‘’> instruction is similar to the

case statement

<xsl:otherwise> instruction is similar to the

default statement

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Xslt – choose Example

Original Xml: <customer> <order id=‘5’> <item><title>Database Management Systems</title></item> </order> </customer> Xslt Stylesheet: <xsl:template match=‘customer’> FUNCTION <xsl:choose> SWITCH <xsl:when test='order/@id'> CASE <single_book_order> <title><xsl:value-of select='order/item/title'/></title> </single_book_order> </xsl:when> <xsl:otherwise><single_book_order><fail/> DEFAULT </single_book_order></xsl:otherwise> </xsl:choose> </xsl:template> Output Xml: <single_book_order><title>Database Management Systems</title></single_book_order>

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Xslt – choose Example 2

Original Xml: <customer> <order> <item><title>Database Management Systems</title></item> </order> </customer> Xslt Stylesheet: <xsl:template match=‘customer’> FUNCTION <xsl:choose> SWITCH <xsl:when test='order/@id'> CASE <single_book_order> <title><xsl:value-of select='order/item/title'/></title> </single_book_order> </xsl:when> <xsl:otherwise><single_book_order><fail/> DEFAULT </single_book_order></xsl:otherwise> </xsl:choose> </xsl:template> Output Xml: <single_book_order><fail/></single_book_order>

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Xslt – for-each Instruction

<xsl:for-each select=‘item’> instruction is

similar to a foreach iterator or a for loop

The select attribute selects a set of elements

from an Xml document

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Xslt – if Instruction

<xsl:if test=‘’> instruction is similar to an if statement

in Java or C++

The test attribute is the if condition:

• True
• statement is true
• test returns an element or attribute.
• False
• statement is false
• test returns nothing

There is no ‘else’, so use the <xsl:choose> operator in

this situation.

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Xslt – for-each and if Example

Original Xml: <basket> <apple color=‘red’ condition=‘yummy’/> <apple color=‘green’ condition=‘wormy/> <apple color=‘red’ condition=‘crisp’/> </basket> Xslt Stylesheet: <xsl:template match=‘basket’> FUNCTION <condition_report> <xsl:for-each select=‘apple’> FOR LOOP <xsl:if test=“contains(@color, ‘red’)”> IF <condition><xsl:value-of select=‘@condition’/></condition> </xsl:if> </xsl:for-each> </condition_report> </xsl:template> Output Xml: <condition_report> <condition>yummy</condition> <condition>crisp</condition> </condition_report>

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Other miscellaneous features

XML docs can have IDs and IDREFs, URIs

• reference to another document or document element

Document Object Model (DOM)

• A tree “object” API for traversing an XML or HTML doc
• Typically for Java

XML Schema is a proposal to replace/augment DTDs

• Has a notion of types and typechecking
• May introduce some notions of IC’s
• Quite complicated, controversial ... not really adopted yet

XML Namespaces

• Can import tag names from others
• Disambiguate by prefixing the namespace name
• I.e. berkeley-eecs:gpa is different from uphoenix:gpa

Lots of other details, tools, etc.

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Reminder: Benefits of Relational

Data independence buys you:

• Evolution of storage -- vs. XML?
• Evolution of schema (via views) – vs. XML?

Database design theory

• IC’s, dependency theory, lots of nice tools for ER

Remember, databases are long-lived and reused

• Today’s “nesting” might need to be inverted tomorrow!

Upshot:

• XML is good for transient data (e.g. messages)
• XML is fine for data that will not get reused in a different

way (e.g. Shakespeare, database output like reports)

• Relational is far cleaner for persistent data

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XML Databases?

Will XML require a new kind of database? Is there a market for new database vendors? Some predictions that we may or may not believe in:

• SQL-99 and XQuery will merge
• Traditional DBMSs will be the serious XML repositories.
• Doesn’t extend their feature set
• Oracle and IBM are paranoid and working hard on XML
• Fighting Oracle and IBM is not a good business plan
• Also a daunting engineering exercise:
• Maybe you have a good XPath engine
• Do you really want to reimplement storage, optimization, 2PL,

ARIES, etc? How do you do row-level locking in XML?

• There will be lots of user tools to help map to/from XML
• Not unlike the “import” tools and “report writers” that already

exist

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Advantages of XML vs. Relational

ASCII makes things easy

• Easy to parse
• Easy to ship (e.g. across firewall, via email, etc.)

Self-documenting

• Metadata (tag names) come with the data

Nested

• Can bundle lots of related data into one message
• (Note: object-relational allows this)

Can be sloppy

• don’t have to define a schema in advance

Standard

• The most interesting thing about XML is that people are interested

in it!

• Lots of free Java tools for parsing and munging XML
• Lots of Microsoft tools (C#) for same

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What XML does not solve

XML doesn’t standardize metadata

• It only standardizes the metadata language
• Not that much better than agreeing on an alphabet
• E.g. my <price> tag vs. your <price> tag
• Mine includes shipping and federal tax, and is in $US
• Yours is manufacturer’s list price in ¥Japan
• XML Schema is a proposal to help with some of this

XML doesn’t help with data modeling

• No notions of IC’s, FD’s, etc.
• In fact, encourages non-first-normal form!

You will probably have to translate to/from XML

• Relational vendors will help with this ASAP
• XML “features” (nesting, ordering, etc.) make this a pain
• Flatten the XML if you want data independence (?)

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XML Summary

XML is an important new standard for representing

data

It is mostly being used for messages between

business apps

• Good because it’s easy to read and transmit
• Can bundle a bunch of related data in one file

Also used for documents, separating content (XML)

from presentation (XSL)

Supports a number of non-first-normal-form

“features”

• Hence troublesome as a “database”

Expect data to be translated to/from XML frequently

• And expect to be given nice tools to help with that.

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More on XML

100 books published in the last 3 years

• Each seems to be 1000 pages

Try some websites

• xml.org provides a business software view of XML
• xml.apache.org has lots of useful shareware for XML
• www.ibm.com/developerworks/xml/ has shareware,

tutorials, reference info

• xml.com is the O’Reilly resource site
• www.w3.org/XML/ is the official XML standard site