1. Extensible Markup and Beyond September 26, 2001 Jeff Derstadt
CS 433 Xml, DTD, XPath, & Xslt
Extensible Markup and Beyond
September 26, 2001
Jeff Derstadt

2. Administration Due: Friday Sept. 28th Logging into Egret Questions?
Relational table creation and summary
See course web site for more details
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3. Overview Xml DTD XPath Xslt A self-describing, hierarchal data model
Standardizing schemas for Xml
XPath
How to navigate and query Xml documents
Xslt
How to transform one Xml document into another Xml document

4. Xml – An Example <class name=‘CS 433’>
<location building=‘Olin’ room=‘255’/>
<professor>Johannes Gehrke</professor>
<ta>Jeff</ta>
<student_list>
<student id=‘ ’>John Smith</student>
<student id=‘ ’>Jane Doe</student>
</student_list>
</class>

5. Xml – Extensible Markup 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

6. 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>

7. Xml – Structure Xml looks like HTML
Xml is a hierarchy of user-defined tags called elements with attributes and data
Data is described by elements, elements are described by attributes
<student id=‘ ’>John Smith</student>
attribute
attribute value
data
closing tag
open tag
element name

8. Xml – Elements <student id=‘999-991’>John Smith</student>
Xml is case and space sensitive
Element opening and closing tag names must be identical
Opening 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/>
attribute
data
closing tag
open tag
element name
attribute value

9. Xml – Attributes
<student id=‘ ’>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).
open tag
element name
attribute
attribute value
data
closing tag

10. Xml - Data <student id=‘999-991’>John Smith</student>
Xml data is any information between an opening and closing tag
Xml data must not contain the ‘<‘ or ‘>’ characters
open tag
element name
attribute
attribute value
data
closing tag

11. Xml – Nesting & Hierarchy
Xml tags can be nested in a tree hierarchy
Xml documents can have only one root tag
Between an opening and closing tag you can insert:
1. Data
2. More Elements
3. A combination of data and elements
<root>
<tag1>
Some Text
<tag2>More</tag2>
</tag1>
</root>

12. Xml – Storage Storage is done just like an n-ary tree (DOM)
<root>
<tag1>
Some Text
<tag2>More</tag2>
</tag1>
</root>
Node
Type: Element_Node
Name: Element
Value: Root
Node
Type: Element_Node
Name: Element
Value: tag1
Node
Type: Element_Node
Name: Element
Value: tag2
Type: Text_Node
Name: Text
Value: Some Text
Node
Type: Text_Node
Name: Text
Value: More

13. Xml vs. Relational Model
<Table>
<Computer Id=‘101’>
<Speed>800Mhz</Speed>
<RAM>256MB</RAM>
<HD>40GB</HD>
</Computer>
<Computer Id=‘102’>
<Speed>933Mhz</Speed>
<RAM>512MB</RAM>
</Table>
Computer Table Id
Speed
RAM HD
101
800Mhz
256MB
40GB
102
933Mhz
512MB

14. DTD – Document Type Definition
A DTD is a schema for Xml data
Xml protocols and languages can be standardized with DTD files
A DTD says what elements and attributes are required or optional
Defines the formal structure of the language

15. DTD – An Example <Basket> <Cherry flavor=‘good’/>
<?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>
<Cherry flavor=‘good’/>
<Apple color=‘red’/>
<Apple color=‘green’/>
</Basket>
<Basket>
<Apple/>
<Cherry flavor=‘good’/>
<Orange/>
</Basket>

16. DTD - !ELEMENT
<!ELEMENT Basket (Cherry+, (Apple | Orange)*) >
!ELEMENT declares an element name, and what children elements it should have
Wildcards:
* Zero or more
+ One or more
Name
Children

17. DTD - !ATTLIST !ATTLIST defines a list of attributes for an element
<!ATTLIST Cherry flavor CDATA #REQUIRED>
<!ATTLIST Orange location CDATA #REQUIRED
color ‘orange’>
!ATTLIST defines a list of attributes for an element
Attributes can be of different types, can be required or not required, and they can have default values.
Element
Attribute
Type
Flag

18. DTD –Well-Formed and Valid
<?xml version='1.0'?>
<!ELEMENT Basket (Cherry+)>
<!ELEMENT Cherry EMPTY>
<!ATTLIST Cherry flavor CDATA #REQUIRED>
Not Well-Formed
<basket>
<Cherry flavor=good>
</Basket>
Well-Formed but Invalid
<Job>
<Location>Home</Location>
</Job>
Well-Formed and Valid
<Basket>
<Cherry flavor=‘good’/>
</Basket>

19. XPath – Navigating Xml
When Xml is stored in a tree, XPath allows you to navigate to different nodes:
Class
<Class>
<Student>Jeff</Student>
<Student>Pat</Student>
</Class>
Student
Student
Text:
Jeff
Text:
Pat

20. XPath – Navigating Xml
Xml is similar to a file structure, but you can select more than one node:
//Class/Student
Class
<Class>
<Student>Jeff</Student>
<Student>Pat</Student>
</Class>
Student
Student
Text:
Jeff
Text:
Pat

21. XPath – Navigating Xml An XPath expression looks just like a file path
Elements are accessed as /<element>/
Attributes are accessed
Everything that satisfies the path is selected
You can add constraints in brackets [ ] to further refine your selection

22. XPath – Navigating Xml Starting Element Attribute Constraint
<class name=‘CS 433’>
<location building=‘Olin’ room=‘255’/>
<professor>Johannes Gehrke</professor>
<ta>Dan Kifer </ta>
<student_list>
<student id=‘ ’>John Smith</student>
<student id=‘ ’>Jane Doe</student>
</student_list>
</class>
Starting Element
Attribute Constraint
Element Path
Selection
Selection Result: The attribute nodes containing
and

23. XPath - Context Context – your current focus in an Xml document Use:
//<root>/…
When you want to start from the beginning of the Xml document

24. XPath - Context XPath: List/Student Class Prof Location List Text:
Gehrke
Attr:
Olin
Student
Student
Text:
Jeff
Text:
Pat

25. XPath - Context XPath: Student Student Text: Jeff Pat Prof Gehrke List
Location
Attr:
Olin
Class

26. XPath – Examples Select all of the red apples:
<Basket>
<Cherry flavor=‘sweet’/>
<Cherry flavor=‘bitter’/>
<Cherry/>
<Apple color=‘red’/>
<Apple color=‘green’/> …
</Basket>
Select all of the red apples:

27. XPath – Examples Select the cherries that have some flavor:
<Basket>
<Cherry flavor=‘sweet’/>
<Cherry flavor=‘bitter’/>
<Cherry/>
<Apple color=‘red’/>
<Apple color=‘green’/> …
</Basket>
Select the cherries that have some flavor:

28. XPath – Examples Select all the apples in the orchard:
<tree>
<apple color=‘red’/>
</tree>
<basket>
<apple color=‘green’/>
<orange/>
</basket>
</orchard>
Select all the apples in the orchard:
//orchard/descendant()/apple

29. 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>

30. 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!)

31. Xslt – A First Look <?xml version='1.0'?>
<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=' version='1.0'>
<xsl:template match='single_book_order'>
<form7957><purchase item='book' property='title' value='{title}‘
quantity='{qty}'/></form7957>
</xsl:template>
</xsl:stylesheet>

32. Xslt – Header Xslt stylesheets MUST include this body:
<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl=' version='1.0'> …
</xsl:stylesheet>

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

34. 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 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.

35. Xslt – Template Matching
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 match=‘box’>
<box/>
<xsl:apply-templates/>
<xsl:template>
Xml
<basket>
<apple color=‘red’/>
<apple color=‘green/>
<box>
<orange taste=‘good’/>
<peach/>
</box>
</basket>
Transformed Xml:
<apple/> <apple/> <apple/>
<box/><apple/>

36. 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

37. 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  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>

38. 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  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>

39. 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

40. 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.

41. 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 ‘red’)”>  IF
<condition><xsl:value-of
</xsl:if>
</xsl:for-each>
</condition_report>
</xsl:template>
Output Xml: <condition_report>
<condition>yummy</condition>
<condition>crisp</condition>

42. Xslt – Other Information
W3C is standardizing XPath and Xslt:
Lot’s of Books. Here’s a suggestion:
D. Martin et al. Professional Xml. Wrox Press, 2000.

43. What’s Next? XSchema XQuery DTDs, but written in XML Will replace DTDs
Fully declarative XML query language
Will be able to do anything you can do with XPath and XSLT, plus a LOT more

44. Xml in Commercial Databases
Many Xml parsers and XSLT engines are availbable
Microsoft, IBM, and Oracle (among others) are adding native Xml support
Native Xml databases

45. URL Tutorials http://msdn.microsoft.com/xml/tutorial/default.asp