Mastering XSLT: Transform XML to XHTML

1. Lecture 6 XSLT (Based on Møller and Schwartzbach, 2006, Chapter 5) CIS336Website design, implementation and management(also Semester 2 of CIS219, CIS221 and IT226) David Meredith d.meredith@gold.ac.uk www.titanmusic.com/teaching/cis336-2006-7.html

2. XML does not contain formatting or layout information • XML provides a general format for representing the logical structure of data • it does not specify how the data should be displayed or presented, for example, in a browser • When the XML file above left is loaded into a browser, it is displayed as at above right • that is, the browser shows the tree structure of the XML file • We need to be able to have precise control over exactly how the data in an XML file is presented or displayed

3. Using CSS with XML • Example above shows how to use cascading style sheets with an XML file • Various problems with doing this: • Cannot print element names so cannot, e.g., label phone number as a phone number • Data always presented in the order it appears in the XML file (e.g., e-mail address has to come before phone number) • Cannot use data stored in attributes • Cannot introduce extra structure like tables

4. Extensible Stylesheet Language (XSL) • XSL consists of • XSL Transformations (XSLT) • a declarative programming language for specifying transformations between XML languages • XSL Formatting Objects (XSL-FO) • a particular target language (like, for example, XHTML) suitable for specifying layout • Behaviour of a stylesheet can be obtained by specifying in XSLT a transformation from an XML language into XHTML (or XSL-FO) • XSLT can also be used to • translate between other pairs of XML languages • extract views of XML data • perform query-like computations

5. XSLT • We'll cover XSLT 2.0 • most current implementations are of XSLT 1.0 • based on XPath 2.0 • XSLT transformations can be executed in standalone tools (e.g., Saxon) • but also supported by modern browsers like Firefox • include processing instruction in XML file to be rendered that links it to an XSLT document • browser then loads XSLT file, executes the transformation and presents the result (usually an XHTML document)

6. Line 2 at top left links XML file with the XSLT file at bottom left • In XSLT file • stylesheet element consists of set of template rules, each within a template element • each template rule has a pattern given in the match attribute • XSLT template rule computes part of the target document • XSLT document at left uses 3 namespaces • xsl is XSLT namespace • b is source namespace (business card language namespace • default is target namespace(XHTML)

7. Output of XSLT transformation on business card

8. XSLT Stylesheets • XSLT stylesheet is a sequence of template rules (see above) • XSLT language defined in an XML Schema http://www.w3.org/2005/02/schema-for-xslt20.xsd • XSLT processor first finds template rule that matches root node and executes corresponding template body

9. Use of XPath 2.0 in XSLT 2.0 • XSLT 2.0 uses XPath 2.0 for • specifying patterns for template rules • e.g., <xsl:template match="b:card"> • selecting nodes for processing • e.g., <xsl:apply-templates select="b:name"/> • computing boolean conditions • e.g., <xsl:if test="b:logo"> • generating text content for the output document • e.g., <xsl:value-of select="b:name/text()"/>

10. Template rules • Template rule matches a part of the input document and constructs a part of the output document • match attribute contains a pattern • Content of template element is a sequence constructor • A collection of template rules in an XSLT stylesheet is evaluated in a context as follows: • the template rules whose patterns match the context are identified • most specific template rule is selected • sequence constructor of selected template rule is evaluated in the context

11. Patterns and matching • XSLT pattern is an XPath 2.0 expression • but not all of XPath 2.0 is allowed within a pattern • pattern can only use abbreviated syntax (e.g., //, @, omission of child::) • it must be either a single expression or a union of expressions, e.g., match="b:name|b:title|b:email|b:phone" match="b:card" • each path step separated by / or // • each step can only use the child or attribute axes (and only in abbreviated syntax) • node tests and predicates can use general syntax • Pattern matches a node, n, if it can be evaluated in a context in which any node in the source document is the context node and the resulting sequence contains n • implies that patterns should be read backwards • e.g., rcp:recipe/rcp:ingredient//rcp:preparation • matches any preparation element that is a descendant of any ingredient element that is a child of a recipe element

12. Patterns and matching: Further examples • students matches • node 1 • student matches • nodes 2 and 10 • students/student matches • nodes 2 and 10 • @grade matches • all grade attribute nodes • student//@grade[. eq "B+"] matches • grade attribute node in node 18 • student[@id="100078"]/age matches • node 12 • result[ancestor::student/@id="100026"][@grade="D"] matches • node 9

13. Sequence Constructors • Simplest sequence constructor is literal sequence of character data nodes and element nodes that do not belong to the XSLT namespace • Stylesheet above always generates the same output document regardless of input document

14. Element and attribute constructors • XSLT stylesheet at left generates same as on previous slide using explicit constructors • Uses XSLT element and attribute constructors • Value of select attribute of attribute constructor (line 14) is an XPath string literal • Explicit constructors and literals can be mixed

15. Computing attribute values • Attribute values can be computed from source document • see line 14 which finds all attributes called bgcolor in source document (of which there will be one)

16. Computing attribute values in literal sequence constructors • {...} in a literal sequence constructor is replaced by atomized value of XPath expression that it is assumed to contain

17. attribute-set element • If collection of attributes often used together, can declare them as an attribute set using the attribute-set XSLT element • Use attribute set by using the use-attribute-sets qattribute • can be used in literals and constructors

18. text and value-of instructions • text instruction can be wrapped around literal character data to preserve whitespace • value-of instruction generates character data from an XPath expression in its select attribute • Example:<xsl:text>2+2 = </xsl:text><xsl:value-of select="2+2"/>generates2+2 = 4whereas2+2 = <xsl:value-of select="2+2"/>generates2+2 =4 • If value of select expression has length greater than 1, then textual versions of the items are concatenated, separated by a single space

19. Constructing processing instructions and comments in the target document <- XSLT document Output document ->

20. apply-templates instruction • apply-templates recursively applies entire stylesheet to nodes specified by the select attribute • default value of select attribute is child::node() • See business card for another example • What do the above stylesheet and source document generate as output?

21. Output of previous transformation

22. for-each instruction • Has same effect as stylesheet on slide 20

23. if instruction • if instruction returns result of sequence constructor in its body if XPath expression in test attribute is true • What is result of running stylesheet above left on XML file at right?

24. Output of transformation on previous slide

25. choose instruction • choose allows various different branches to be tried in order • What is the output of the above stylesheet when the source document is as at right?

26. Output of transformation on previous slide

27. name and mode attributes • template node may have other attributes besides match: name • provides a name for the template rule which allows it to be called like a function • if name attribute is present, match attribute might not be mode • only allowed if match attribute is present • restricts template rules that can match a given node • a mode is either a QName or #default • value of mode attribute is either • a space-separated sequence of modes • #all indicating all possible modes

28. Use of mode attribute • apply-templates instruction may use a mode attribute to only consider those template rules that have a corresponding mode attribute • What is the output when the above stylesheet is applied to the XML file on the right?

29. Result of previous transformation