Xml, DTD, XPath, & XsltExtensible Markup and Beyond

OverviewXml A self-describing, hierarchal data model

DTD Standardizing schemas for Xml

XPath How to navigate and query Xml documents

Xslt How to transform one Xml document into

another Xml document

Xml – An Example<class name=‘CS 433’>

<location building=‘Olin’ room=‘255’/><professor>Johannes Gehrke</professor><ta>Dan Kifer </ta><student_list><student id=‘999-991’>John Smith</student><student id=‘999-992’>Jane Doe</student></student_list>

</class>

Xml – Extensible Markup Language

Language A way of communicating information Markup Notes or meta-data that describe your

data or language Extensible Limitless ability to define new

languages or data sets

Xml – What’s The Point?You can include your data and a description of what the data represents This is useful for defining your own

language or protocol Example: Chemical Markup Language

<molecule><weight>234.5</weight><Spectra>…</Spectra><Figures>…</Figures>

</molecule>

Xml – StructureXml looks like HTMLXml is a hierarchy of user-defined tags called elements with attributes and dataData is described by elements, elements are described by attributes<student id=‘999-991’>John Smith</student>

closing tagattribute

attribute value

dataopen tagelement name

Xml – Elements<student id=‘999-991’>John Smith</student>

Xml is case and space sensitiveElement opening and closing tag names must be identicalOpening tags: “<” + element name + “>”Closing tags: “</” + element name + “>”Empty Elements have no data and no closing tag: They begin with a “<“ and end with a “/>”

<location/>

closing tagattribute

attribute value

dataopen tagelement name

Xml – Attributes<student id=‘999-991’>John Smith</student>

Attributes provide additional information for element tags.There can be zero or more attributes in every element; each one has the the form:

attribute_name=‘attribute_value’- There is no space between the name and the “=‘”- Attribute values must be surrounded by “ or ‘ characters

Multiple attributes are separated by white space (one or more spaces or tabs).

closing tagattribute

attribute value

dataopen tagelement name

Xml - Data<student id=‘999-991’>John Smith</student>

Xml data is any information between an opening and closing tagXml data must not contain the ‘<‘ or ‘>’ characters

closing tagattribute

attribute value

dataopen tagelement name

Xml – Nesting & HierarchyXml tags can be nested in a tree hierarchyXml documents can have only one root tagBetween an opening and closing tag you can insert:

1. Data2. More Elements3. A combination of data and elements

<root> <tag1> Some Text <tag2>More</tag2> </tag1></root>

Xml – Storage Storage is done just like an n-ary tree (DOM)

<root> <tag1> Some Text <tag2>More</tag2> </tag1></root>

NodeType: Element_NodeName: -Value: Root

NodeType: Element_NodeName: -Value: tag1

NodeType: Text_NodeName: TextValue: More

NodeType: Element_NodeName: ElementValue: tag2

NodeType: Text_NodeName: TextValue: Some Text

Xml vs. Relational Model

Id Speed RAM HD101

800Mhz

256MB

40GB

102

933Mhz

512MB

40GB

Computer Table

<Table> <Computer Id=‘101’> <Speed>800Mhz</Speed> <RAM>256MB</RAM> <HD>40GB</HD> </Computer> <Computer Id=‘102’> <Speed>933Mhz</Speed> <RAM>512MB</RAM> <HD>40GB</HD> </Computer></Table>

DTD – Document Type Definition

A DTD is a schema for Xml dataXml protocols and languages can be standardized with DTD filesA DTD says what elements and attributes are required or optional Defines the formal structure of the

language

DTD – An Example<?xml version='1.0'?><!ELEMENT Basket (Cherry+, (Apple | Orange)*) >

<!ELEMENT Cherry EMPTY><!ATTLIST Cherry flavor CDATA #REQUIRED>

<!ELEMENT Apple EMPTY><!ATTLIST Apple color CDATA #REQUIRED>

<!ELEMENT Orange EMPTY><!ATTLIST Orange location ‘Florida’>

-------------------------------------------------------------------------------- <Basket>

<Apple/> <Cherry flavor=‘good’/> <Orange/></Basket>

<Basket> <Cherry flavor=‘good’/> <Apple color=‘red’/> <Apple color=‘green’/></Basket>

DTD - !ELEMENT<!ELEMENT Basket (Cherry+, (Apple | Orange)*)

>

!ELEMENT declares an element name, and what children elements it should have Wildcards: * Zero or more + One of more

Name Children

DTD - !ATTLIST<!ATTLIST Cherry flavor CDATA #REQUIRED>

<!ATTLIST Orange location CDATA #REQUIREDcolor ‘orange’>!ATTLIST defines a list of attributes for an elementAttributes can be of different types, can be required or not required, and they can have default values.

Element Attribute Type Flag

DTD –Well-Formed and Valid

<?xml version='1.0'?><!ELEMENT Basket (Cherry+)>

<!ELEMENT Cherry EMPTY><!ATTLIST Cherry flavor CDATA #REQUIRED>

--------------------------------------------------------------------------------

Well-Formed and Valid<Basket> <Cherry flavor=‘good’/></Basket>

Not Well-Formed<basket> <Cherry flavor=good></Basket>

Well-Formed but Invalid<Job> <Location>Home</Location></Job>

XPath – Navigating XmlWhen Xml is stored in a tree, XPath allows you to navigate to different nodes:

Class

Student Student

Text:Jeff

Text:Pat

<Class> <Student>Jeff</Student> <Student>Pat</Student></Class>

XPath – Navigating XmlXml is similar to a file structure, but you can select more than one node:

//Class/Student Class

Student Student

Text:Jeff

Text:Pat

<Class> <Student>Jeff</Student> <Student>Pat</Student></Class>

XPath – Navigating Xml An XPath expression looks just like a file path Elements are accessed as /<element>/ Attributes are accessed as @attribute Everything that satisfies the path is selected You can add constraints in brackets [ ]

to further refine your selection

XPath – Navigating Xml<class name=‘CS 433’> <location building=‘Olin’ room=‘255’/> <professor>Johannes Gehrke</professor> <ta>Dan Kifer </ta> <student_list> <student id=‘999-991’>John Smith</student> <student id=‘999-992’>Jane Doe</student> </student_list></class>

//class[@name=‘CS 433’]/student_list/student/@id

Starting Element

Attribute Constraint

Element Path

SelectionSelection Result: The attribute nodes containing 999-991 and 999-992

XPath - ContextContext – your current focus in an Xml document Use:

//<root>/… When you want to start from the

beginning of the Xml document

XPath - Context

Student Student

Text:Jeff

Text:Pat

Prof

Text:Gehrke

ListLocation

Attr:Olin

Class

XPath: List/Student

XPath - Context

Student Student

Text:Jeff

Text:Pat

Prof

Text:Gehrke

ListLocation

Attr:Olin

Class

XPath: Student

XPath – Examples<Basket>

<Cherry flavor=‘sweet’/><Cherry flavor=‘bitter’/><Cherry/><Apple color=‘red’/><Apple color=‘red’/><Apple color=‘green’/>…

</Basket>

Select all of the red apples://Basket/Apple[@color=‘red’]

XPath – Examples<Basket>

<Cherry flavor=‘sweet’/><Cherry flavor=‘bitter’/><Cherry/><Apple color=‘red’/><Apple color=‘red’/><Apple color=‘green’/>…

</Basket>

Select the cherries that have some flavor://Basket/Cherry[@flavor]

XPath – Examples<orchard> <tree> <apple color=‘red’/> <apple color=‘red’/> </tree> <basket> <apple color=‘green’/> <orange/> </basket></orchard>

Select all the apples in the orchard://orchard/descendant()/apple

Xslt – Transforming XmlAmazon.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>

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!)

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>

Xslt – HeaderXslt 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>

Xslt – TemplatesXslt stylesheets are a collection of templates Templates are like functions The body of a template is the output

of a transformation

Xslt - TemplatesYou define a template with the

<xsl:template match=‘’> instructionYou call a template with the

<xsl:apply-templates select=‘’> instruction1. All elements or attributes that satisfy the 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.

Xslt – Template MatchingStylesheet<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>

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>

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

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>

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>

Xslt – for-each Instruction<xsl:for-each select=‘item’> instruction is similar to a foreach iterator or a for loopThe select attribute selects a set of elements from an Xml document

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.

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>

Xslt – Other Information W3C is standardizing XPath and Xslt:

http://www.w3.org/TR/xslt.html

http://www.w3.org/TR/xpath.html

Lot’s of Books. Here’s a suggestion: D. Martin et al. Professional Xml. Wrox

Press, 2000.

URL Tutorialshttp://msdn.microsoft.com/xml/tutorial/default.asp

http://www.ils.unc.edu/~kempa/inls259/xml/

http://www.geocities.com/SiliconValley/Peaks/5957/10minxml.html