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Extensible Stylesheet Language (XSL)

Extensible Stylesheet Language (XSL). The XSL Standard. XSL consists of 3 parts: XPath (navigation in documents) XSLT (transformation of documents) XSLFO (FO for formatting objects ) A rather complex language for typesetting (e.g., for preparing text for printing) It will not be taught.

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Extensible Stylesheet Language (XSL)

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  1. Extensible Stylesheet Language (XSL)

  2. The XSL Standard XSL consists of 3 parts: • XPath(navigation in documents) • XSLT(transformation of documents) • XSLFO(FO for formatting objects) • A rather complex language for typesetting (e.g., for preparing text for printing) • It will not be taught

  3. XML Path Language(XPath)

  4. XML example revisited:

  5. <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries> world.xml

  6. The root is implicit (Does not appear in the text of the XML document) The XML DOM Model

  7. <!ELEMENTcountries(country*)> <!ELEMENTcountry(name,population?,city*)> <!ATTLISTcountrycontinentCDATA#REQUIRED> <!ELEMENTname (#PCDATA)> <!ELEMENTcity (name)> <!ATTLISTcitycapital(yes|no) "no"> <!ELEMENTpopulation (#PCDATA)> <!ATTLISTpopulationyearCDATA#IMPLIED> <!ENTITYeu"Europe"> <!ENTITYas"Asia"> <!ENTITY af"Africa"> <!ENTITY am"America"> <!ENTITY au"Australia"> world.dtd

  8. The XPath Language • XPath expressions are used for addressing elements (nodes) of an XML document • Used in XSLT(next subject today)and in XQuery(a query language for XML) • The syntax resembles that of the Unix file system • But the semantics have some substantial differences /countries/country[population>10000000]

  9. /countries/country[population>10000000] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  10. //country[@continent="Asia"]/city world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  11. XPath Expressions • An XPath expression (or just XPath for short) matches paths in the XML tree • An absolute path begins with the root of the document • Starts with "/" (or "//") • For example,/countries/country/city, //city • A relative path begins with a context node that is defined by the application that uses the XPath • For example, city/name, or ./name

  12. Applying XPath to XML • Formally, the result of applying an XPath e to an XML document (or a context node in the document) isthe list of all nodes n in the document, such that e matches the path from the root (or the context node) to n • The order in the list is defined by the order of the nodes in the document

  13. XPath Steps and Axis • An XPath describes a sequence of steps that together characterize a path • A step is defined by an axis that specifies a tree relationship between nodes • More particularly, the axis describes how to get from the current node to the next one • For example, parent-child, child-parent, ancestor-descendant, etc. • Consecutive steps are separated by /

  14. Child Axis • A child axis has the simple form tagName • Go to an element child with the tag tagName • For example, • /tagName matches the tagName child of root • city/name • /countries/country/city • The child axis * matches every tag • For example: /*/*/city,*/name

  15. Child-Axis Examples /countries

  16. Child-Axis Examples /countries/country/city

  17. Child-Axis Examples city/name Context

  18. Child-Axis Examples /*/country/* An attribute is not an element child!

  19. Self and Descendant-or-Self • The self axis “.” denotes the identity relationship • That is, the step “remain in the current node” • /countries/country/.≡/countries/country • country/./city ≡ country/city • The descendant-or-self axis means: either stay in the current node or go to some descendant of the current node • descendant-or-self:node(), • // is a shotrcut notation for /descendant-or-self:node()/ • For example, country//name

  20. /countries//name Descendant Examples

  21. .//* Descendant Examples Context

  22. Other Axis Types • The parent axis “..” denotes the parent relationship • That is, the step “go to the parent of the current node” • For example, //name/../population • XPath has more axis types (denoted by a different syntax from the ones shown earlier): • descendant • ancestor • ancestor-or-self • following-sibling • preceding-sibling • …

  23. Referring Attributes • The attribute axis is denoted @attName • That is, “go to the attribute attName of the current node” • The operator @* matches every attribute

  24. //country/@continent Attribute Examples

  25. Attribute Examples @continent Context

  26. //@* Attribute Examples

  27. XPath Predicates • Predicates in XPath are used for filtering out steps • For example, //city[@captial="yes"] will match only capital cities • Formally, given a predicate [PExpr], the expression PExpr is transformed into a Boolean value and the step is taken only if this value is true • The node reached in the last step is the context node • XPath has a rather rich language for predicate expressions; we only demonstrate common ones

  28. //country[./population>10000000] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries> • The XPath ./population is transformed into a number by taking its embedded text • The XPath ./population is relative to the current node (i.e., country) in the path • Equivalent to //country[population>10000000]

  29. //country[.//city] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries> An XPath evaluates to true if and only if its result is not empty

  30. //country[//city] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries> Why?

  31. //country[population[.>3000000 and @year>2003]] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  32. //country[name="Israel" or name="Spain"]/population world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  33. //country/city[2] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries> • A number acts as an index • That is, the number n evaluates to true if n is the position of the node among all those reached in the last step (i.e., city)

  34. Functions • Inside XPath predicates, you can use a set of predefined functions • Here are some examples: • last() – returns the number of nodes obtained from the last axis step • position() – returns the position of the node in the list of nodes satisfying the last axis step • name() – returns the name (tag) of the current node • count(XPath) – returns the number of nodes satisfying XPath

  35. //country/city[last()] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  36. //city[position()<2] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  37. //*[name()="city" or name()="country"] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  38. //*[starts-with(name(),“c")] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  39. //country[count(./city)>=1] world.xml <?xmlversion="1.0"?> <!DOCTYPEcountriesSYSTEM"world.dtd"> <countries> <country continent="&as;"> <name>Israel</name> <population year="2001">6199008</population> <city capital="yes"><name>Jerusalem</name></city> <city><name>Ashdod</name></city> </country> <country continent="&eu;"> <name>France</name> <population year="2004">60424213</population> </country> </countries>

  40. Final Remarks • The syntax of XPath that was presented here is the abbreviated syntax • For example, city/../@nameis an abbrv. of child::city/parent::node() /attribute::name • More details on XPath: • XPath tutorial in W3Schools • XPath W3C Recommendation

  41. XSL Transformations (XSLT) An Example: Useful Links in the DBI site

  42. XSLT • XSLT is a language for transforming XML documents into other XML documents • For example, XHTML, WML • Can also transform XML to general text documents, e.g., SQL programs • An XSLT program is itself an XML document (called an XSL stylesheet) that describes the transformation process for input documents

  43. XSLT Processors XSLT Processor

  44. Web Pages – The Whole Picture Web Page Data Presentation Knowledge Doc. Structure XSL XHTML Style CSS XML Dynamics JavaScript

  45. <?xml version="1.0" encoding="ISO-8859-1"?> <catalog> <cdcountry="UK"> <title>Dark Side of the Moon</title> <artist>Pink Floyd</artist> <price>10.90</price> </cd> <cdcountry="UK"> <title>Space Oddity</title> <artist>David Bowie</artist> <price>9.90</price> </cd> <cdcountry="USA"> <title>Aretha: Lady Soul</title> <artist>Aretha Franklin</artist> <price>9.90</price> </cd> </catalog> catalog.xml

  46. Valid XML! Commands are XML elements with the namespace xsl Includes XHTML elements <?xml version="1.0" encoding="ISO-8859-1"?> <xsl:stylesheetversion="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:templatematch="/"> <html> <head><title>cd catalog</title></head> <body><h1>This is a cd catalog!</h1></body> </html> </xsl:template> </xsl:stylesheet> catalog.xsl

  47. Applying XSL Stylesheets to XML There are several ways of applying an XSL stylesheet to an XML document: • Directly applying anXSLT processor to the XML document and the XSL stylesheet • Calling an XSLT processor from within a program • Adding to the XML document a link to the XSL stylesheet and letting the browser do the transformation • The resulting XHTML document is shown, not the original XML

  48. Processing XSL in Java You can use the XALAN package of Apache in order to process XSL transformations javaorg.apache.xalan.xslt.Process -INmyXmlFile.xml -XSLmyXslFile.xsl -OUTmyOutputFile.html

  49. How Does XSLT Work? • An XSL stylesheet is a collection of templates that are applied to source nodes (i.e., nodes of the given XML) • Each template has a match attributethat specifies to which source nodes the template can be applied • Each source node has a template that matches it • The current source node is processed by applying a template that matches this node • When processing a node, it is possible to recursively process other nodes, e.g., the children of the current node • Finally, the XSLT processor simply processes the root node of the document (that matches /)

  50. Templates • A template has the form <xsl:templatematch="pattern"> ... </xsl:template> • The content of a template consists of • XML elements (e.g., XHTML) and text that are copied to the result • XSL elements (<xsl:…>) that are actually instructions • The syntax for the pattern is a subset of XPath

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