Comprehensive Guide to XSLT: Conditionals, Numbering, Variables, and Templates

1. XSLT II Robin Burke ECT 360

2. Outline • Conditionals • Numbering • Functions and operators • Variables and parameters • Named and recursive templates

3. Conditional nodes • XSLT supports two kinds of conditional elements: • <xsl:if> • <xsl:choose> • If is only if-then (no else) • Choose is more general

4. Example • if • choose

5. Comparison operators

6. Predicates • XPath expressions • test for a condition • result = set of nodes that fulfill that condition

7. Example • from last week

8. Numbering • Number nodes using: • <xsl:number> • position() • Using position(): • Nodes are numbered by position in result document • Can be used in conditional statements

9. Number element • Nodes are numbered according to position in source document • Attributes: • value=expression: any XPath expression that evaluates to a number (i.e. position()) • count=pattern: specifies which nodes to count • level=type: tree level for nodes to count; can be any, single, or multiple

10. USING <XSL:NUMBER> • Attributes: • from=pattern: pattern indicates where numbering should restart • format=pattern: pattern indicates number format • grouping-size, grouping-separator: indicate how digits are grouped and separator character

11. Example • numbering

12. XPath numerical functions

13. XPath string functions

14. XPath operators

15. Example • Calculating the average

16. Number format • XPath function format-number • Syntax: format-number(value, format) • Example: format-number(56823.847, '#,##0.00') displays 56,823.85

17. Number format syntax

18. Decimal format • XSL element for defining number formats • Named decimal format passed as argument to format-number

19. Variables • Not variable! • User-defined name that stores a particular value or object • Types: • number • text string • node set • boolean • result tree fragment

20. Using variables • Syntax: <xsl:variable name=“name” select=“value”/> • Example: <xsl:variable name=”Months” select=”12” /> • Names are case-sensitive • Value only set once upon declaration • Enclose text strings in single-quotes

21. Using variables • Value can be XPath expression • Value can be XML fragment • Syntax: <xsl:variable name=”Logo”> <img src=”logo.gif” width=”300” height=”100” /> </xsl:variable>

22. Variable reference • Syntax: $variable-name • Example: $Months • Referencing tree fragments: • Do not use $variable-name • Use <xsl:copy-of> to reference value

23. COPYING

24. Global variables • Can be referenced from anywhere within the style sheet • Must be declared at the top level of the style sheet, as a direct child of the <xsl:stylesheet> element • Must have a unique variable name • Evaluated only once when stylesheet is invoked

25. Local variables • Referenced only within template • Can share name with other local or global variable • Reevaluated when template is used

26. Examples • average • numbering

27. Parameters • Similar to variables, but: • Value can be changed after it is declared • Can be set outside of scope • Syntax: <xsl:param name=“name” select=“value”/> • Example: <xsl:param name=”Filter” select=”'C103'” /> • To reference: $param-name

28. External parameters • Depends on XSLT processor • Some work by appending parameter value to url • Command line processors allow external parameter setting: • MSXML • Saxon

29. Template parameters • Local in scope • Created inside <xsl:template> element • Used to pass parameters to template

30. Idea • Called template • contains param definitions • Calling template • place <xsl:with-param> element in <xsl:apply-templates> element • or <xsl:call-template> element • Syntax: <xsl:with-param name=“name” select=“value”/> • No error if calling param name does not match template param name

31. Named template • Template not associated with node set • Collection of commands that are accessed from other templates in the style sheet • Syntax: <xsl:template name="name"> XSLT elements </xsl:template>

32. Calling named templates • Syntax: <xsl:call-template name=”name”> <xsl:with-param /> <xsl:with-param /> ... </xsl:call-template>

33. Example

34. Functional programming • Functional programming language: • Relies on the evaluation of functions and expressions, not sequential execution of commands • Different from C family of languages • LISP, Scheme, ML

35. Templates as functions • A template supplies a result fragment • incorporated into the final document • think of this as substitution • function call replaced by result

36. Iteration • How to handle iteration with templates? • stars for ratings • Possibilities • convert numbers into node sets • weird since node sets are supposed to come from the document • recursive templates

37. Recursion • Recursion • base case • when do I stop? • recursive case • how do I bite off one piece • call template again with the rest

38. Example • Template: star(rating) • desired output: # stars = # in rating • Base case: • rating = 0 • output: nothing • Recursive case • rating > 0 • output: * plus result of star (rating-1)

39. Example, cont'd • star(3) • replaced by * star(2) • replaced by ** star(1) • replaced by *** star(0) • ***

40. Pseudocode • stars (n) • if n = 0 return '' • else • return '*' + stars(n-1)

41. Recursive pattern • Syntax with <xsl:if>: <xsl:template name=”template_name”> <xsl:param name=”param_name” select=”default_value” /> ... <xsl:if test=”stopping_condition”> ... <xsl:call-template name=”template_name”> <xsl:with-param name=”param_name” select=”new_value” /> </xsl:call-template> ... </xsl:if> </xsl:template>

42. Example

43. Another example • "best rated" jeep supplier • Finding maximum • built into XSLT 2.0

44. Recursive statement?

45. What about the name?

46. Homework #5 • Case 1 from Chapter 7 • Plus doing it "correctly" with CSS