Übung 5 Klaus Schild,

Transcription

1 Übung 5 1

2 Übung 5 Fragen zur Vorlesung XSLT? XSLT in Depth XSLT Programming Musterfragen Musterlösung XSLT for transformation from content to presentation 2

3 XSLT in Depth 3

4 Valid XSLT <xsl:stylesheet> </xsl:stylesheet> <xsl:stylesheet xmlns:xsl=" Transform" > </xsl:stylesheet> <xsl:stylesheet version="1.0" > xmlns:xsl=" Transform" </xsl:stylesheet> 4

5 Valid XSLT <xsl:stylesheet version="1.0" > xmlns:xsl=" Transform" </xsl:stylesheet> <name> </name> <first_name>john</first_name> <last_name>smith</last_name> 5

6 Valid XSLT John Smith How come? 6

7 Never forget about the. Default templates - Are ALWAYS used by the XSLT processor - Can t be switched off, only OVERRIDDEN <xsl:template match="* /"> <xsl:apply-templates/> </xsl:template> <xsl:template <xsl:value-of select="."/> </xsl:template> <xsl:template match="processinginstruction() comment()" /> 7

8 Default templates <name> <first_name>john</first_name> <last_name>smith</last_name> </name> root (/) name first_name last_name John Smith 8

9 Overriding templates If a match exists in the stylesheet, that template will override the default template <xsl:template match="name"> <! - Do Nothing --> </xsl:template> overrides <xsl:template match="* /"> <xsl:apply-templates/> </xsl:template> 9

10 Overriding templates (2) So what about this? Does the more specific template override the more general? <xsl:template match="name"> <! - Do Nothing --> </xsl:template> <xsl:template match="name[2]"> <xsl:apply-templates/> </xsl:template> is overriden by 10

11 Overriding templates (3) And what about this? What happens if the name element in the second position has also a lang attribute with the value en? <xsl:template match="name[@lang='en']"> <! - Do Nothing --> </xsl:template> <xsl:template match="name[2]" <xsl:apply-templates/> </xsl:template>??? 11

12 Template priority If more than one template rule with the same import precedence matches a given node. - Import precedence is default template rules, explicitly imported rules and then rules in the actual stylesheet the one with the highest priority is chosen - Rules with match patterns of a single element or attribute name have priority 0 - Rules with match patterns of prefix:* have priority Rules with match patterns which have only a wildcard test (*,@*,node() ) have priority Rules with any other patterns, e.g. with location paths or predicates, have priority

13 Template priority (2) It is an error if two or more template rules match a node and have the same priority - Most XSLT processors choose the LAST template rule rather than signal an error One can explicitly give a template a priority <xsl:template match=" " priority="1"> How to execute multiple rules on the same node? - Use a more general match on a template rule - Within the rule, make the specific node selection - You can use named templates rather than matching on the selected node 13

14 Overriding by import You can use <xsl:import href="import.xsl"/> However, imported templates have less precedence than templates in the main stylesheet To force the processor to use BOTH an imported template and a template in the main stylesheet: <xsl:apply-imports /> The problem is that imports must be top level elements and come before all other elements, hence are always overridden The alternative is to include templates at the top level but ANYWHERE in the stylesheet, such as right at the end <xsl:include href="import.xsl"/> 14

15 XSLT and namespaces XSLT processors are namespace-aware - Patterns must identify namespaces of elements <name xmlns=" </name> <first_name>john</first_name> <last_name>smith</last_name> <xsl:template match="name"> <! - Do Nothing --> </xsl:template> 15

16 XSLT and namespaces <name xmlns=" </name> <first_name>john</first_name> <last_name>smith</last_name> <xsl:stylesheet xmlns=" <xsl:template match="name"> <! - Do Nothing --> </xsl:template> </xsl:stylesheet> 16

17 XSLT and namespaces <aa:name xmlns:aa=" </aa:name> <aa:first_name>john</aa:first_name> <aa:last_name>smith</aa:last_name> <xsl:stylesheet xmlns:zz=" <xsl:template match="zz:name"> <! - Do Nothing --> </xsl:template> </xsl:stylesheet> 17

18 XSLT Programming 18

19 Did you know XSLT is Turing-complete - meaning? Turing-completeness: - Computational system that can compute every Turingcomputable function - Such functions represent the notion of algorithm, i.e. a finite program should be able to compute them - They are used to measure models of computation All general programming languages are Turing-complete - Hence: XSLT is as expressive as such languages! 19

20 Proving XSLT s programming power XSLT is usually referred to as a declarative programming language For example, one can state z = y + 3 The variable z now has the value of y increased by 3 A variable, once declared, can not change value (stateless) In XSLT it looks like this: <xsl:variable name="z" select="$y + 3" /> 20

21 Higher order functions in XSLT Functions can be implemented in template references - Templates in XSLT correspond to functions - Named templates are called by xsl:call-template - Parameters are declared on a template with xsl:param - Parameter values are set when a template is called using xsl:with-param In XSLT one has to call a template specifically by name - You can t provide a template name by variable - Hence you can t really dynamically call templates 21

22 Template references Define templates which perform some function, e.g. <xsl:template name="2times"> <xsl:param name = "a" /> <xsl:value-of select = "2 * $a" /> </xsl:template> <xsl:template name="3plus"> <xsl:param name = "a" /> <xsl:value-of select = "3 + $a" /> </xsl:template> 22

23 Template references (2) Now define a template which accepts as parameter an input value, instantiates the two function templates, passing to each instantiation the input in the template s parameter and as result gives the sum of the outputs. mysum(x)=(2*x)+(3+x) Call mysum(3): <xsl:call-template name = "mysum" > <xsl:with-param name = "x" select = "3" /> </xsl:call-template> 23

24 Template references (3) <xsl:template name = "mysum" > <xsl:param name = "x" /> <xsl:variable name="v1"> <xsl:call-template name = "2times" > <xsl:with-param name= "a" select="$x" /> </xsl:call-template> </xsl:variable> <xsl:variable name="v2"> <xsl:call-template name = "3plus" > <xsl:with-param name="a" select="$x" /> </xsl:call-template> </xsl:variable> <xsl:value-of select="$v1 + $v2"/> </xsl:template> 24

25 Template references (4) How about printing a certain number of dots, where the number is not known at compile time? In C, it could look like this: void printdots(int n) { int i; for (i = 0; i < n; i++) { printf("."); } } 25

26 Recursive programming What most programming languages can accomplish with loops must be solved in functional languages like XSLT with recursion Recursion is a powerful programming construct for solving particular classes of problem (divide and conquer) Usual construction: <xsl:template name=" "> Parameters Test Do something or not (Another Test) Either generate new parameter values call template recursively Or end </xsl:template> 26

27 Recursion example I presently have an XML tag stored as so: <rating> 7 </rating> It is essentially for rating a product out of a possible score of 10. What I want to do is to convert it like this: Rating: where the "7" will be made BOLD. 27

28 Recursion example Define the starting state <xsl:template name="ratings"> <xsl:param name="limit" select="10"/> <xsl:param name="this" select="1"/> <xsl:param name="emph"/> $this is the parameter that will be tested $emph is the parameter to be tested against (when the template is called, it shall be set to the value that is to be placed in bold) $limit is the exit condition 28

29 Recursion example Define the test <xsl:choose> <xsl:when test="$this=$emph"> <b> <xsl:value-of select="$this"/></b> </xsl:when> <xsl:otherwise> <xsl:value-of select="$this"/> </xsl:otherwise> </xsl:choose> 29

30 Recursion example Define the recursion. Don t forget an exit condition! <xsl:if test="$this < $limit"> <xsl:call-template name="ratings"> <xsl:with-param name="limit" select="$limit"/> <xsl:with-param name="this" select="$this+1"/> <xsl:with-param name="emph" select="$emph"/> </xsl:call-template> </xsl:if> </xsl:template> 30

31 Musterfragen 31

32 Frage 1 Which of the following XSLT elements will apply any matching templates to all the children of the current node? A. <xsl:apply-templates select="node()" /> B. <xsl:call-template name="*" /> C. <xsl:apply-templates /> D. <xsl:call-template /> E. <xsl:apply-templates name="*" /> 32

33 Frage 2 <?xml version="1.0" encoding="utf-8"?> <periodictable> <chemicalelement symbol="ag"> <atomicnumber>47</atomicnumber <atomicweight> </atomicweight </chemicalelement> Which is the output from </periodictable> <xsl:copy/>? A. <chemicalelement/> B. <chemicalelement symbol="ag"/> C. <chemicalelement symbol="ag"> </chemicalelement> D

34 Frage 3 <?xml version="1.0" encoding="utf-8"?> <periodictable> <chemicalelement symbol="ag"> <atomicnumber>47</atomicnumber <atomicweight> </atomicweight </chemicalelement> Which is the output from </periodictable> <xsl:copy-of select="." />? A. <chemicalelement/> B. <chemicalelement symbol="ag"/> C. <chemicalelement symbol="ag"> </chemicalelement> D

35 Frage 4 <?xml version="1.0" encoding="utf-8"?> <periodictable> <chemicalelement symbol="ag"> <atomicnumber>47</atomicnumber <atomicweight> </atomicweight </chemicalelement> Which is the output from </periodictable> <xsl:value-of select="." />? A. <chemicalelement/> B. <chemicalelement symbol="ag"/> C. <chemicalelement symbol="ag"> </chemicalelement> D

36 Frage 5 <?xml version="1.0" encoding="utf-8"?> <A> <B c="123"> <C /> <D>text</D> </B> <D> <E>more text</e> <F c="246" /> </D> <F a="369" /> </A> <xsl:template match="a"> <xsl:apply-templates /> </xsl:template> <xsl:template match="b D F"> <xsl:value-of select="@*" /> </xsl:template> Which is the output? A. Nothing B. 123 text more text C D

37 Frage 6 <?xml version="1.0" encoding="utf-8"?> <A> <B c="123"> <C /> <D>text</D> </B> <D> <E>more text</e> <F c="246" /> </D> <F a="369" /> </A> <xsl:template match="b D F"> <xsl:if test="node()/text()"> <xsl:value-of select="." /> </xsl:if> </xsl:template> Which is the output? A. Nothing B. text C. text more text D. 123 text more text

38 Frage 7 <?xml version="1.0" encoding="utf-8"?> <A> <B c="123"> <C /> <D>text</D> </B> <D> <E>more text</e> <F c="246" /> </D> <F a="369" /> </A> <xsl:template match="d"> <xsl:apply-templates select="f" /> </xsl:template> <xsl:template match="f"> <xsl:value-of select="@*" /> </xsl:template> Which is the output? A. Nothing B. text more text C. text D

39 Musterlösung sung des Übungsblattes 4 39

40 Beispieltransformation <document xmlns=" > <title>beginning XML</title> <author>hunter et al.</author> <chapter name="chapter 1"> <section>chap. 1_1</section> <section>chap. 1_2</section> <section>chap. 1_3</section> </chapter> <chapter name="chapter 2"> <section>chap. 2_1</section> <section>chap. 2_2</section> </chapter> <chapter name="chapter 3"> <section>chap. 3_1</section> <section>chap. 3_2</section> <section>chap. 3_3</section> <section>chap. 3_4</section> </chapter> </document> 40

41 Ergebnisdokument 41

42 Nötige strukturelle Transformation 42

43 Klasse der Ursprungsdokumente 43

44 Grundstruktur der Lösung für jedes Element außer ns:section ein Template match="ns:document": alle document Elemente, die Namensraum zugeordnet sind 44

45 Erzeugung der HTML-Grundstruktur 45

46 Transformation von title und author Was passiert, wenn title oder author nicht vorhanden ist? 46

47 ns:title <h1>, ns:author <h2> Was passiert, wenn title oder author Kind-Elemente haben? 47

48 Select. or text()? <xsl:template match="p"> <DIV> <xsl:copy-ofof select="."/> </DIV> <DIV> <xsl:copy/> </DIV> <DIV> <xsl:value-of select="."/> </DIV> </xsl:template> <source> <p id="a12">compare <B>these constructs</b>. </p> </source> <DIV> <p id="a12">compare <B>these constructs</b>. </p> </DIV> <DIV> <p/> </DIV> <DIV> Compare these constructs. </DIV> oder mit "text()" statt "." <DIV> Compare </DIV> 48

49 Spaltenüberschriften erzeugen 49

50 Grundstruktur der Tabelle erzeugen Beachte: select="ns:chapter" meint alle Kind-Elemente ns:chapter 50

51 Spaltenüberschriften <TH> erzeugen 51

52 Zeilen <TR> erzeugen Für N von 1 bis zur maximalen Anzahl von sections: Erzeuge <TR> mit <TD>s, die Nte section von jedem chapter enthalten! 52

53 Erzeuge Zeile N! 53

54 Erzeuge Zeile N! Beachte: für ns:section kein Template definiert Was passiert hier ohne ein solches Template? 54

55 Vordefinierte Templates 1. vordefiniertes Template realisiert rekursiven Aufruf des Prozessors, wenn kein Template anwendbar ist: <xsl:template match="* /"> <xsl:apply-templates/> </xsl:template> 2. vordefiniertes Template kopiert PCDATA und Attribut-Werte des aktuellen Knotens in das Ergebnisdokument: <xsl:template <xsl:value-of select="."/> </xsl:template> 55

56 Vermeide <TD/>! selbstschließende Elemente <TD/> vermeiden, da HTML <TD></TD> erwartet 56

57 Rekursion: Erzeuge Zeile N+1 57

58 Und der eigentliche Aufruf mit N=1 58

59 XSLT for content to presentation 59

60 Content to presentation Besides content-to-content transformations, XSLT is often used to transform a content format (i.e. some XML document) into a presentation format The output mustn t be well formed XML, it could be HTML or some other unstructured textual format However, there are XML-based presentation formats (XHTML, SVG, SMIL) XML-to-XML transformation is preferable - As XSLT templates work on a XML input structure, it is an easier mapping to a XML output structure - It is also easier to check output validity 60

61 RSS to SMIL <smil> <head> <layout> <root-layout width="450 height="450"/> <region id="top" top="0" left="0" width="450" height="100"/> <region id="text" top="100" left="0" width="250" height="100"/> <region id="desc" top="200" left="0" width="250" height="250" /> <region id="img" top="100" left="250" width="200" height="350" /> </layout> </head> <body>... </body> </smil> 61

62 RSS to SMIL (2) <rss> <channel> <title>.</title> <item> <title>star City</title> <enclosure> </enclosure> <description>.</description> </item> <item> <title>star City</title> <enclosure> </enclosure> <description>.</description> </item> </channel> </rss> <smil> <head> <layout>... </layout> </head> <body> <text src=".." region="top" /> <seq begin="0s"> <par dur="10s"> <text src=".." region="text" /> <text src=".." region="desc" /> <image src=".." region="img" /> </par> <par dur="10s"> </par> </seq> </body> </smil> 62

63 RSS to SMIL (3) <rss> <channel> <title>.</title> <item> <title>star City</title> <enclosure> </enclosure> <description>.</description> </item> <item> <title>star City</title> <enclosure> </enclosure> <description>.</description> </item> </channel> </rss> <smil> <head> <layout>... </layout> </head> <body> <text src=".." region="top" /> <seq begin="0s"> <par dur="10s"> <text src=".." region="text" /> <text src=".." region="desc" /> <image src=".." region="img" /> </par> <par dur="10s"> </par> </seq> </body> </smil> 63

64 The XSLT <xsl:template match="/"> <xsl:apply-templates select="rss" /> </xsl:template> Why not just start writing e.g. template match="//item"? Because we want to ensure we are transforming a RSS document, and not just some XML document with item elements! 64

65 The XSLT (2) <xsl:template match="rss"> <smil> <head> <layout>... </layout> </head> <body> <xsl:apply-templates select="title" /> <seq> <xsl:apply-templates select="item" /> </seq> </body> </smil> </xsl:template> 65

66 The XSLT (3) <xsl:template match="title"> <text src="data:,{.}" region="top" /> </xsl:template> Reminder: <xsl:value-of select="." /> returns the string value of the element node (the text within the element tags) We can t put the value-of element inside an output element, so we use an attribute value template This means placing the XPath expression inside curly braces {} Btw the data: scheme needs to escape spaces which XPath function could be used here? 66

67 The XSLT (4) <xsl:template match="item"> <par dur="10s"> <text src="data:,{title}" region="text" /> <text src="data:,{description}" region="desc" /> <image region="img" /> </par> </xsl:template> Reminder: Template will be called for each item element in document order Why not use separate templates for the child elements of item? We assumed enclosures were images, how could we write <image>, <audio> or <video> elements based on the value of enclosure s type attribute? 67

68 Viewing in the browser To have a RSS (or any XML) document shown in the browser with style rules applied <?xml-stylesheet href="rss.xsl" type="text/xsl" media="screen"?> Generally used with stylesheets with (X)HTML output If the browser is correctly configured, a SMIL output should be opened in a SMIL player For our example (with inline text) you need to use Real Player 68