XML

BIS4430 – unit 10

XML Origins• Extensible Markup Language (XML) 1998

• Inspired by Standard Generalized Markup Language (SGML) and HTML.

• SGML defines how any given markup language can be formally specified

• HTML combines markup from several categories: Text Structuring Tags <H1>,

• Formatting Tags <B>, Linking <A>, <IMG>, and Data Input Tags <FORM>,<INPUT>

The key benefits of XML are:

· Readable by both humans and computers

· Facilitates the optimal structuring of data

· Free and/or inexpensive

· Widely available

· Easy to learn

· Supported by all major software vendors

XML vs HTML

<book><title>XML by Example</title><author>Sean McGrath</author><publisher>Prentice Hall, Inc.</publisher><publish_date>1999</publish_date><description>Building E-commerce Applications with XML</description></book>

<P>Book</P><P>Title: XML by Example</P><P>Author: Sean McGrath</P><P>Publisher: Prentice Hall, Inc.</P><P>Date Published: 1999</P><P>Description: Building E-commerce Applications </P>

Namespaces

• Namespaces resolve ambiguous element tag names, in order to associate correct elements in an XML document.

Namespaces

OrderInfo.xml

<Order_Info>

<Name>John Dow</Name>

<Address>19 Footlong Court</Address>

<City>Tallwood</City>

<Order>Cigars</Order>

<Date>31-12-02</Date>

</Order_Info>

BillingInfo.xml

<Billing_Info>

<Name>Angela Dow</Name>

<Payment>Visa</Payment>

<Number>12344</Number>

</Billing_Info>

Namespaces: Explicit<order: Order_Info xmlns:order =”http://www.mdx.ac.uk/~ariel/order”

xmlns:bill=“http://www.mdx.ac.uk/~ariel/bill” >

<order:Name >John Dow</order:Name>

< order:Address>19 Footlong Court</ order:Address>

< order:City>Tallwood</ order:City>

< order:Order>Cigars</ order:Order>

< order:Date>31-12-02</ order:Date>

<bill:Billing_Info >

< bill:Name >Angela Dow</bill:Name>

< bill:Payment>Visa</ bill:Payment>

< bill:Number>12344</ bill:Number>

</ bill:Billing_Info>

</ order:Order_Info>

XML Parsers

• XML processor is used to read XML documents and provide access to their content and structure

• It is assumed that an XML processor is doing its work on behalf of another module, called the application

XML Processing

Parsers• Nonvalidating – they simply verify if the

document adheres to rules of the XML syntax i.e. whether the XML document is well formed

• Validating – these parsers read in XML documents, check if they are well formed and verify their compliance with a specified XML schema or other validation set, i.e. they verify if the XML document is valid.

Content Access

Converting XML with XSLT

• XSL technologies allow to transform XML documents into various formats, such as PDF( Adobe Acrobat Reader), WML for wireless devices, and into HTML.

Retrieve the element content

• <xsl:value-of select="element name goes here"/>

• <xsl:if test= "boolean-expression-goes here">....</xsl:if>

<xsl:for-each select="element name goes here">

<!--processing instructions go here-->

</xsl:for-each>

Example

xsl:for-each select="student_list/student">

<b>Name: </b><xsl:value-of select="name"/><p/><b>ID: </b><xsl:value-of select="student_ID"/><p/><b>Studying : </b><xsl:value-of select="major"/>

</xsl:for-each>

Database Integration

• XML Database Mapping– More description on next slide

• Using Native XML Databases– Store XML data in XML document– Data is serialised

XML Database Mapping

• Associate elements in an XML document with the relational database fields.

• Query the database with SQL

• Convert results into an XML document

• Popular solution: Java & JDBC

XML Web Services

• Advantages of Web Services– Component independence

– Component based

– XML based interfaces