XML Technology in E-Commerce

Sheet 1XML Technology in E-Commerce 2001 Lecture 6

XML Technology in E-Commerce

Lecture 6

XPointer, XSLT


• XPointer– Purpose: specifying fragment identifiers for XML

documents;

– Points and Ranges;

– Extensions to XPath;

– XPointer Forms;

• XSLT– Rendering XML;

– XSL Suite;

– Example;

– XSLT Elements;

Lecture Outline


XML

XML Namespaces

XPath

XPointerXSLT

XLink

XML Schema

XML Languages

Parser

DOMSAX

Software Application

Overview


Fragment Identifiers

• The part after “#” character in URIs is called fragment identifier:http://some.site.net/path/myFile.html#introduction;

http://some.site.net/path/myXML.xml#id001’

• Fragment identifier specifies retrieval action on the resource;

• The syntax and interpretation of fragment identifiers are media dependent;


XPointer

• Specifies language for expressing fragment identifiers for XML documents;

• Addresses internal structures of XML documents;• Extends XPath;• Provides facilities for:

– selection of a specific position in an XML document;

– selection of a range in an XML document;

• Current status: Working Draft;

http://www.w3.org/TR/xptr


Points and Ranges

img

competition

results photos

imgname name name

John Smith D. Warwick M. Douglas

Point 1Container: TextIndex: 5

Range Point 2Container: TextIndex: 2

Range

Point 1Container: photosIndex: 0

Point 2Container: photosIndex: 2

DOM representation of a sample XML document:


XPointer Terms

• Point - position in XML information. Consists of container node and index;

• Range - all the information between two end points;• Location - XPath’s nodes plus points and ranges;• Location set - ordered list of locations. Usually a

result of XPointer expression;

Location and Location set are a generalization of XPath’s Node and Node set


Extensions to XPath

• XPath allows locating subset of nodes;• XPointer allows locating parts that are not nodes.

Points and Ranges extend the notion of Node;• XPointer expression yields object of type location

set;• Evaluation is made relatively to the root node of an

XML document.• The test for points and ranges uses point and range

keywords;


XPointer Forms

• Full XPointers:xpointer(//contact[@id=“author02”])

xlink:href=“/contacts.xml#xpointer(//contact[@id=‘author02’])”

• Bare names: short syntax for id() function:xpointer(id(“author02”))

xlink:href=“/contacts.xml#author02”


XPointer Functions

• range-to(expr). The start point is the context location. The end point is returned by the evaluation of expr;

xpointer(id("chap1")/range-to(id("chap2")))

• string-range(location-set, string). For each location

in location-set, the function returns string ranges

that match the string argument;

string-range(//title,”Introduction")[4]


Summary on XPointer

• Specifies fragment identifiers in URIs;• Still unstable, working draft status;• Based on XPath;• Implementations:

– Fujitsu XLink Processor;– libxml;

– 4XPointer;


• XPointer– Purpose;

– Points and Ranges;

– Extensions to XPath;

– XPointer Forms;

• XSLT– Rendering XML;

– XSL Suite;

– Example;

– XSLT Elements;

Lecture Outline


Rendering XML• HTML specifies how the documents are rendered;

• In general, XML-based languages do not specify how the documents are rendered;

Problem: How to render XML documents on different devices?

XMLDocument


Rendering XML• Solutions:

– Attach CSS stylesheet;

– Transformation in another document language understood by a particular device;

XMLDocument

CSSStylesheet Browser

Transformation

FODocument

HTML

WML

?

PDF


XSL• XSL - Extensible Stylesheet Language. Language

for expressing stylesheets;

• Two parts:– XSLT (Extensible Stylesheet Language for

Transformations): Language for specifying transformations of XML documents. W3C Recommendation;

– XSL Formatting Objects (XSL FO): XML vocabulary for expressing formatting semantics. W3C Candidate Recommendation;

• XSL W3C site:http://www.w3.org/Style/XSL/


Example• What we have:<book isbn="999-99999-9-x">

<title>Deitel XML Primer</title><author>

<firstName>Paul</firstName><lastName>Deitel</lastName>

</author><chapters>

<preface num="1" pages="2">Welcome</preface><chapter num="1" pages="4">Easy XML</chapter><chapter num="2" pages="2">XML Elements?</chapter><appendix num="1" pages="9">Entities</appendix>

</chapters><media type="CD"/>

</book>


• What we want:Example

<html>

<head>

<title>ISBN - 999-99999-9-x - Deitel XML Primer</title>

</head>

<body>

<h1>Deitel XML Primer</h1>

<h2>Deitel, Paul</h2>

<table border="1">

<tr><td align="right">Preface 1</td>

<td>Welcome (2 pages )</td></tr>

<tr><td align="right">Chapter 1</td>

<td>Easy XML (4 pages )</td></tr>

<tr><td align="right">Chapter 2</td>

<td>XML Elements? (2 pages )</td></tr>

<tr><td align="right">Appendix 1</td>

<td>Entities (9 pages )</td></tr>

</table>

</body>

</html>


XSLTBasic Terms

• Transformation expressed in XSLT is called stylesheet;

• Stylesheet transforms a source tree into a result tree;

• Stylesheet is a set of template rules;• Rules have two parts:

– Pattern: selects nodes from the source tree. Uses XPath syntax;

– Template: instantiated in order to form a part of the source tree;

• Source and result tree roughly conform to the XPath data model;


XSLTGeneral Processing Scheme

Stylesheetexpressed in XSLT

XSLTProcessor

Source treeResult tree


Source tree Result tree

Instantiates

Instantiates

Stylesheet

XSLTRule matching and Template Instantiation

Rule 1

Rule 2

Rule 3

Matches

Matches

Matches


Demo

• Demo - modified version of Deitel 12.5, fig. 12.8 and 12.9, page 327;

• Tools:– XML Spy 3.5;

– XSLT Processor:• MSXML 3

• Or any downloadable extension for Spy, e.g. Infoteria iXSLT or SAXON;

• Demo files:– book.xml;

– style.xsl;


Demo Explained

• Stylesheet root element:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

…………………………………………………………..

</xsl:stylesheet>

• Stylesheet contains elements from XSLT namespace. They are recognized and executed by the XSLT processor;

• Stylesheet includes non-XSLT elements. They can reside in their own namespace;


Template Rules

• First, the root node of the source tree is mapped to html element, which is the root element of all HTML

documents, i.e. the root node of the result tree: <xsl:template match="/">

<html>

<xsl:apply-templates/>

</html>

</xsl:template>

• <xsl:apply-templates/> processes all children of the

current node. In our case the current node is the root

node;


Getting Text from Source Tree

<xsl:template match="book"> <head> <title>ISBN - <xsl:value-of select="@isbn"/> - <xsl:value-of select="title"/></title> </head> <body> <h1><xsl:value-of select="title"/></h1> <h2><xsl:value-of select="author/lastName"/>, <xsl:value-of select="author/firstName"/></h2> ………………………………………………… ………………………………………………… </body> </xsl:template>

•Element value-of:


Repetition• Creating the table and the first row:<xsl:template match=“book”>

…………

<table border = "1">

<xsl:for-each select = "chapters/preface">

<tr><td align = "right">Preface <xsl:value-of select = "@num"/></td>

<td><xsl:value-of select = "."/>

(<xsl:value-of select = "@pages"/> pages )</td>

</tr>

</xsl:for-each>

• for-each element instantiates the template for each node selected by the pattern. The selected node becomes the current node for the template;


Creating Elements• We can reformulate a part of the previous template by

using element XSLT element:

<tr><td align = "right">Preface <xsl:value-of select = "@num"/></td>

<xsl:element name=“td”>

<xsl:value-of select = "."/>

(<xsl:value-of select = "@pages"/> pages )

</xsl:element>

</tr>

• The template contained in the element, becomes the content of the element with name td in the result tree;


Creating Attributes• We can reformulate a part of the previous template by

using attribute XSLT element: <tr><td align = "right">Preface <xsl:value-of select = "@num"/></td>

<td><xsl:value-of select = "."/> (<xsl:value-of select = "@pages"/> pages )

</td>

</tr>

<tr>

<xsl:element name=“td”>

<xsl:attribute name=“align”>right</xsl:attribute>

Preface <xsl:value-of select = "@num"/>

</xsl:element>

<td><xsl:value-of select = "."/> (<xsl:value-of select = "@pages"/> pages )

</td>

</tr>


Copying Nodes

• XSLT element copy copies the current node and includes it in the result tree;

• The attributes and children are not copied;• The template of the copy element generates their

content;• Example - identity transformation:

<xsl:template match="@*|node()">

<xsl:copy>

<xsl:apply-templates select="@*|node()"/>

</xsl:copy>

</xsl:template>


DemoUsing XSLT to test the XPath expressions

• Demo - uses the file from Deitel Ex11.3, fig. 11.15, page 316;

• Tools:– XML Spy 3.5;

– XSLT Processor:• MSXML 3

• Or any downloadable extension for Spy, e.g. Infoteria iXSLT or SAXON;

• Demo files:– transactions.xml;

– xpath.xsl;


Processing Model• At each step we have a list of source nodes;• At the first step the list contains the root node;• Each node is processed by finding the template rules

with pattern that matches the node;• Only one rule is selected;• The template rule is instantiated with the node as a

current node;• XSLT instructions in the template are executed. They

add new source nodes for processing;• The process stops when the list of source nodes is

empty;


Summary on XSLT• Powerful transformation language for XML

documents based on XML syntax;• Allows multiple representations of a single

document;• Available software implementations:

– MSXML 3;

– iXSLT for Infoteria;

– Saxon;

– Xalan-Java, Xalan-C++, part of Apache XML Project;

– XT;


Summary on XSLT (2)

Read: Deitel 12;

Assignment: Deitel Ex 12.3, Ex 12.7, page 351. For some

hints see the course web site.

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XML Technology in E-Commerce