411 REFERENCE · Wikibooks

XML - Managing Data Exchange/XLink

Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.

XPath CSS Learning objectives Learn different techniques of implementing XLink's in XML create a custom XLink learn the functionality behind various XLink parameters sponsored by: The University of Georgia Terry College of Business Department of Management Information Systems Introduction Through the use of Uniform Resource Identifiers (URI's), an XLink allows elements to be inserted into XML documents that create links between resources such as documents, images, files and other pages. An XLink is similar in concept to an HTML hyperlink, but is more powerful and flexible. This chapter will be a general overview of the XLink syntax. It will also provide exposure to some of XLink's basic concepts. For the full XLink specification, see the latest version of the standard at: http://www.w3.org/TR/xlink XLink XLinks create a linking relationship between two or more resources. They allow for any XML element, image, text or markup files to be specified in the link. By using a method similar to the centralized formatting of XSL stylesheets, XLinks allow a document's hyperlinks to be isolated and centralized in a separate document. As a linked document's addresses changes, the XLink remains functional. The use of XLink requires the declaration of the XLink namespace. This namespace provides the global attributes for type, href, role, arcrole, title, show, actuate, label, from and to. The following example would make the prefix xlink available within the tourGuide element. <tourGuide xmlns:xlink="http://www.w3.org/1999/xlink"> ... </tourGuide> XLink global attributes The following table outlines the attributes that can be used with the xlink namespace. The global attributes are type, href, role, arcrole, title, show, actuate, label, from, and to. The table also includes descriptions of how the attributes can be used. Exhibit 1: Table of global attributes Attributes Description and Valid Values type Describes the meaning of an item simple - basic format similar to html linkage extended - more complex than simple types with multi functional format resource - provides local resources locator - provides remote resources arc - provides the ability to traverse from one resource to another title - readable name or explanation of link href Location of resource value is URI role Description of XLink's content value is URI describes the element whose role it is arcrole Description of XLink's content value is URI describe the relationship between the two sides of the arc title Name displayed, usually short description of link show Describes behavior of the browser once the XLink has been actuated and loaded new - load in a new window or frame replace - load in same window or frame embed - replace the current item other - look for information elsewhere none - not specified actuate Specifies when resource is retrieved or link processing occurs onRequest - when user requests the link onLoad - when page is loaded other - looks for information elsewhere none - not specified label, from & to Specifies link direction XML schema The following XML schema defines a tour guide that contains at least one city. Each city contains one or more attractions. The name of each attraction is an XLink. Exhibit 2: XML schema for TourGuide <?xml version="1.0" encoding="UTF-8"?>   <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" elementFormDefault="unqualified" xmlns:xlink="http://www.w3.org/1999/xlink"> <xsd:element name="tourGuide"> <xsd:complexType> <xsd:sequence> <xsd:element name="city" type="cityDetails" minOccurs="1" maxOccurs="unbounded" /> </xsd:sequence> </xsd:complexType> </xsd:element>  <xsd:complexType name="cityDetails"> <xsd:sequence> <xsd:element name="cityName" type="xsd:string"/> <xsd:element name="adminUnit" type="xsd:string"/> <xsd:element name="country" type="xsd:string"/> <xsd:element name="continent"> <xsd:simpleType> <xsd:restriction base="xsd:string"> <xsd:enumeration value="Asia"/> <xsd:enumeration value="Africa"/> <xsd:enumeration value="Australia"/> <xsd:enumeration value="Europe"/> <xsd:enumeration value="North America"/> <xsd:enumeration value="South America"/> <xsd:enumeration value="Antarctica"/> </xsd:restriction> </xsd:simpleType> </xsd:element> <xsd:element name="population" type="xsd:integer"/> <xsd:element name="description" type="xsd:string"/> <xsd:element name="attraction" type="attractionDetails" minOccurs="1" maxOccurs="unbounded"/> </xsd:sequence> </xsd:complexType> <xsd:complexType name="attractionDetails"> <xsd:sequence>  <xsd:element name="attractionName" xlink:type="simple"/> <xsd:element name="attractionDescription" type="xsd:string"/> <xsd:element name="attractionRating" type="xsd:integer"/> </xsd:sequence> </xsd:complexType> </xsd:schema> XML document The following XML document shows how the XLink, attractionName, defined in the XML schema, is used in an XML document. Note that it is necessary to include xlink:href="" within the attribute tags in order to define the linked website. Exhibit 3: XML document for TourGuide.xsd (using XLink) <?xml version="1.0" encoding="UTF-8"?>   <?xml-stylesheet href="TourGuide.xsl" type="text/xsl"?> <tourGuide xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xlink="http://www.w3.org/1999/xlink" xsi:noNamespaceSchemaLocation="TourGuide.xsd"> <city> <cityName>Atlanta</cityName> <adminUnit>Georgia</adminUnit> <country>USA</country> <continent>North America</continent> <population>425000</population> <description>Atlanta is the capital of and largest city in the U.S. state of Georgia.</description> <attraction>  <attractionName xlink:href="http://www.georgiaaquarium.org/"> Georgia Aquarium </attractionName> <attractionDescription>World’s Largest Aquarium</attractionDescription> <attractionRating>5</attractionRating> </attraction> <attraction>  <attractionName xlink:href="http://www.high.org/"> High Museum of Art </attractionName> <attractionDescription>The High Museum of Art, founded in 1905 as the Atlanta Art Association, is the leading art museum in the Southeastern United States.</attractionDescription> <attractionRating>4</attractionRating> </attraction> <attraction>  <attractionName xlink:href="http://www.underground-atlanta.com/"> Underground Atlanta </attractionName> <attractionDescription> Go beneath the streets of a bustling downtown, to the heart of a great American city. Underground Atlanta is at the center of it all.</attractionDescription> <attractionRating>2</attractionRating> </attraction> </city> <city> <cityName>Tampa</cityName> <adminUnit>Florida</adminUnit> <country>USA</country> <continent>North America</continent> <population>303000</population> <description>Tampa is a major United States city located in Hillsborough County, on the west coast of Florida.</description> <attraction>  <attractionName xlink:href="http://www.buschgardens.com/buschgardens/fla/default.aspx"> Bush Gardens </attractionName> <attractionDescription>The nation's fourth largest zoo, Bush Gardens is where you can see African animals roaming free and an exciting amusement park featuring its world-famous rides like Kumba and the new inverted roller-coaster, Montu.</attractionDescription> <attractionRating>5</attractionRating> </attraction> <attraction>  <attractionName xlink:href="http://www.plantmuseum.com/"> Henry B. Plant Museum </attractionName> <attractionDescription>Discover a museum which transports you to turn-of-the-century Florida.</attractionDescription> <attractionRating>1</attractionRating> </attraction> </city> </tourGuide> XML stylesheet The following XML stylesheet displays the contents of the XML document. Exhibit 4: XML stylesheet TourGuide <?xml version="1.0" encoding="UTF-8"?>   <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xlink="http://www.w3.org/1999/xlink" exclude-result-prefixes="xlink" version="1.0"> <xsl:output method="html"/>  <xsl:template match="*[@xlink:type = 'simple' and @xlink:href]"> <a href="{@xlink:href}"> <xsl:apply-templates/> </a> </xsl:template> <xsl:template match="/"> <html> <head> <title>Tour Guide XLink Example</title> </head> <body> <h2>Cities</h2> <xsl:apply-templates select="tourGuide"/> </body> </html> </xsl:template>  <xsl:template match="attractionName"> <a href="{@xlink:href}"> <xsl:value-of select="."/> </a> </xsl:template> <xsl:template match="tourGuide"> <table border="1" width="100%"> <xsl:for-each select="city"> <tr> <td> <br/> <xsl:text>City: </xsl:text> <xsl:value-of select="cityName"/> <br/> <xsl:text>County: </xsl:text> <xsl:value-of select="adminUnit"/> <br/> <xsl:text>Continent: </xsl:text> <xsl:value-of select="continent"/> <br/> <xsl:text>Population: </xsl:text> <xsl:value-of select="population"/> <br/> <xsl:text>Description: </xsl:text> <xsl:value-of select="description"/> <br/> <br/> </td> </tr> <tr> <td> <xsl:text>Attraction: </xsl:text> </td> <td> <xsl:text>Attraction Description: </xsl:text> </td> <td> <xsl:text>Attraction Rating: </xsl:text> </td> </tr> <xsl:for-each select="attraction"> <tr> <td>  <xsl:apply-templates select="attractionName"/> </td> <td> <xsl:value-of select="attractionDescription"/> </td> <td> <xsl:value-of select="attractionRating"/> </td> </tr> </xsl:for-each> </xsl:for-each> </table> </xsl:template> </xsl:stylesheet> Summary XLink is an extremely versatile specification that standardizes the process for linking to other data sources. Not only does XLink support unidirectional linking similar to an anchor tag in HTML but also can be used to create bidirectional links. Additionally, XLink allows for the linkage from any XML element. This gives great freedom to the developer. Exercises Answers