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4 Document Transformations

4 Document Transformations. XSLT (1.0 W3C Rec , Nov 1999; XSLT 2.0 Rec , Jan 2007) A language for transforming XML documents initial main purpose to support XSL formatting used mainly for independent transformations (esp. XML → HTML)

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4 Document Transformations

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  1. 4 Document Transformations • XSLT (1.0 W3C Rec, Nov 1999; XSLT 2.0 Rec, Jan 2007) • A language for transforming XML documents • initial main purpose to support XSL formatting • used mainly for independent transformations(esp. XML → HTML) • Our goal: to understand the basic model and central features of XSLT • Overview and an example • Data model and processing model 4: Overview of XSLT

  2. XSLT: Overview • XSLT uses XML syntax for expressing transformations • of a document source tree into a result tree • result and source are separate trees • by template rules • Each template rule has • apattern (matched against nodes of the source tree) • a templateas a body • instantiated to create fragments of the result tree 4: Overview of XSLT

  3. Overview of XSLT Transformation 4: Overview of XSLT

  4. Style Sheets and Template Rules • Anxsl:stylesheet(orxsl:transform) consists of template rules: <xsl:template match="Pattern"> Template<!--well-formed XML!--> </xsl:template> • Rule applied to nodes of the source tree matched by the Pattern • expressed using XPath (XML Path Language) • Template consists of • literal result tree fragments (elements, text), and • XSLT instructions for controlling further processing conventional XSLT namespace prefix 4: Overview of XSLT

  5. XPath in a Nutshell • XPath 1.0 W3C Rec. 11/99 (2.0 Rec. 1/07) • a compact non-XML syntax for addressing parts of XML documents as node-sets( sequences in 2.0) • used also in other W3C languages • Specs for hyperlinks in XML: XLink (Rec. '01) and XPointer (Rec. '03) • XQuery (Rec. 1/07; extends XPath 2.0) • also typical operations on strings, numbers and truth values 4: Overview of XSLT

  6. Early impressions of XSLT 2.0 • Somewhat more advanced & flexible than 1.0 • Complexity of 1.0 vs. 2.0 specs (as pages): Data Model ~ 80 XPath 2.0 ~100 Funcs & opers ~160 XSLT 2.0 ~280---------------------------------- ~620 • XPath 1.0 ~ 30 • XSLT 1.0 ~ 90 • ------------------------ • Total ~ 120 4: Overview of XSLT

  7. An XSL transformation example • Transform below document to HTML: <?xml-stylesheet type="text/xsl" href="walsh.xsl" ?> <!-- Modified from an example by Norman Walsh --> <doc><title>My Document</title> <para>This is a <em>short</em> document.</para> <para>It only exists to <em>demonstrate a <em>simple</em> XML document</em>.</para> <figure><title>My Figure</title> <graphic fileref="myfig.jpg"/></figure> </doc> 4: Overview of XSLT

  8. Result (edited for readability) <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>A Document</TITLE></HEAD> <BODY> <H1>My Document</H1> <P>This is a <I>short</I> document.</P> <P>It only exists to <I>demonstrate a <B>simple</B> XML document</I>.</P> <DIV> <B>Figure 1. </B> <BR> <IMG src="myfig.jpg"><B>My Figure</B> </DIV> </BODY> </HTML> 4: Overview of XSLT

  9. Example style sheet begins <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="/"> <!-- rule for root --> <HTML><HEAD><TITLE>A Document</TITLE></HEAD> <BODY> <!-- process root's children here: --> <xsl:apply-templates /> </BODY> </HTML> </xsl:template> <xsl:template match="doc/title"> <H1><xsl:apply-templates /></H1> </xsl:template> 4: Overview of XSLT

  10. Example (parasand emphs) <xsl:template match="para"> <P><xsl:apply-templates /></P></xsl:template> <xsl:template match="em"> <I><xsl:apply-templates /></I></xsl:template> <xsl:template match="em/em"> <B><xsl:apply-templates /></B></xsl:template> 4: Overview of XSLT

  11. Example (figures) <xsl:template match="figure"> <!-- Insert a bold caption of form 'Figure Num. ' by counting all figures in the document: --><DIV><B>Figure <xsl:number level="any" count="figure"/>. </B> <BR /> <!-- Process the children of figure, --> <!-- the 'graphic' child first: --> <xsl:apply-templates select="graphic" /> <!-- then the 'title' child: --> <xsl:apply-templates select="title" /> </DIV> </xsl:template> 4: Overview of XSLT

  12. Example (end of style sheet) <xsl:template match="graphic"> <IMG src="{@fileref}" /> <!-- Assign the value of attribute 'fileref' to attribute 'src' --> </xsl:template><xsl:template match="figure/title"> <B> <xsl:apply-templates /> </B></xsl:template> </xsl:stylesheet> 4: Overview of XSLT

  13. Result (edited for readability) <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>A Document</TITLE></HEAD> <BODY> <H1>My Document</H1> <P>This is a <I>short</I> document.</P> <P>It only exists to <I>demonstrate a <B>simple</B> XML document</I>.</P> <DIV> <B>Figure 1. </B> <BR> <IMG src="myfig.jpg"><B>My Figure</B> </DIV> </BODY> </HTML> 4: Overview of XSLT

  14. What use of XSL(T)? • XSL can be used in different ways • for offline document formatting • produce, say, PDF from XML by an XSL style sheet (using XSLT + XSL formatting objects) • for offline document manipulation • transform XML into other form (XML/HTML/text) using XSLT • for online document delivery • on a Web server • in a Web browser (if the browser supports) 4: Overview of XSLT

  15. XSLT in online document delivery • XSLT in a browser • defines rendering of XML documents • supported by current major browsers • transformation of XML to HTML on the fly in browser • XSLT on a Web server • an HTTP request served by transforming XML on the fly to HTML (or other format) on the server 4: Overview of XSLT

  16. Main Aspects of XSLT • Data model • How is document data viewed in XSLT? • Selection mechanism • How are document parts selected for processing? • Matching • How are the template rules selected? • Processing model • How does the XSLT execution proceed? 4: Overview of XSLT

  17. Data Model of XSLT and XPath • Documents are viewed as treesmade of seven types of nodes: • root (additional parent of document element) • element nodes • attribute nodes • text nodes • comments, processing instructions and namespaces • NB: Entity references are expanded-> no entity nodes 4: Overview of XSLT

  18. XSLT/XPath document trees • Defined in Sect. 5 of XPath 1.0 spec • for XSLT/XPath 2.0 & XQuery in their joint Data Model • Element nodes have elements, text nodes, comments and processing instructions of their (direct) content as their children • NB: attribute nodes are not children (but have a parent) • the value of an element node is the concatenation of its text-node descendants 4: Overview of XSLT

  19. XSLT/XPath Trees • Similar to the DOM, with slight differences: • 7 vs 12 node types • value of an element: its full textual content (In DOM: null) • names for text nodes, comment nodes, etc are empty(In DOM: "#text", "#comment", etc.) • Document order of nodes: • root node first, otherwise according to the order of the first character of the XML markup for each node • > element node precedes it's attribute nodes, which precede any content nodes of the element 4: Overview of XSLT

  20. 1st 2nd 4th 3rd 7th 5th or 6th 5th or 6th XSLT/XPath trees: Example <article>Written by <fig file="pekka.jpg" caption="The Lecturer" /> the lecturer.</article> null in DOM 4: Overview of XSLT

  21. Main Aspects of XSLT • Data model • Selection mechanism • How are document parts selected for processing? • A: With XPath expressions • Matching • Processing model 4: Overview of XSLT

  22. XPath Expressions • Used for selecting source tree nodes, conditional processing, and generating new text content • return node-sets, truth values, numbers or strings • can select any parts of source tree (node-set) for processing, using … • Location paths • the most characteristic of XPath expressions • evaluated with respect to a context node • often the current node matched by the template pattern • result: set of nodes selected by the location path 4: Overview of XSLT

  23. Location paths • Consist of location steps separated by '/' • each step produces a set of nodes • steps evaluated left-to-right, each node in turn as context node • path begins with ‘/’ -> root is the first context node • Complete location step: AxisName::NodeTest ([PredicateExpr])* • axis specifies the tree relationship between the context node and the selected nodes • node test restricts the type and and name of nodes • filtered further by 0 or more predicates 4: Overview of XSLT

  24. Location steps: Axes • In total 13 axes (~ directions in tree) • for staying at the context node: • self • for going downwards: • child, descendant, descendant-or-self • for going upwards: • parent, ancestor, ancestor-or-self • for moving towards start/end of the document: • preceding-sibling, following-sibling, preceding, following • “Special” axes • attribute, namespace 4: Overview of XSLT

  25. The simplest axis,self:: XPath Axes and Their Orientation • Ordinary axes oriented away from context node(attribute and namespace axes are unordered) • the position() for the closest node = 1 • for the most remote node, position() = last() 4: Overview of XSLT

  26. XPath Axes and Their Orientation • parent::(exists for every node except the root) 1 Context node: 4: Overview of XSLT

  27. ancestor-or-self:: XPath Axes and Their Orientation • ancestor:: 4: Overview of XSLT

  28. XPath Axes and Their Orientation • child:: 4: Overview of XSLT

  29. descendant-or-self:: XPath Axes and Their Orientation • descendant:: 4: Overview of XSLT

  30. following-sibling:: XPath Axes and Their Orientation • preceding-sibling:: 4: Overview of XSLT

  31. preceding:: XPath Axes and Their Orientation • following:: 4: Overview of XSLT

  32. Location paths: Node tests • Location paths: [/]Step/.../Step, where • Step = [axis::] NodeTest ('['Pred']')* • Node tests (slightly simplified) • Name: any element node with that Name(on an attribute axis, any attribute node with that Name) • *: any element(any attribute node on an attribute axis) • text(): any text node • comment(): any comment node • processing-instruction(): any processing instruction • node(): any node of any type 4: Overview of XSLT

  33. Location paths: Abbreviations • Abbreviations in location steps • 'child::' can be omitted • 'attribute::'can be shortened to '@' • 'self::node()'can be shortened to '.'(period) • 'parent::node()'can be shortened to '..' • Predicate '[position()=n]' for testing occurrence position n can be shortened to '[n]' • '/descendant-or-self::node()/'shortened to '//' ->Syntax resembles slightly Linux/Unix file path names 4: Overview of XSLT

  34. A A Semantics of Location Paths (example) context node {2, 5, 7} 1 5 2 7 B C final value: {2} B 3 4 6 C 8 B "txt" */node()/parent::B[child::A] value after each step: {3, 4, 6, 8} {2, 5, 7} 4: Overview of XSLT

  35. Location path examples (1) • chapchildren of current node: ./chap(or simply chap, or./child::*[name()='chap']) • The document element (child element of root node):/* • Elements chapteranywhere (below the root): //chapter(.//chapter->anywhere below the context node) • All chapters oftypeAorB: //chapter[@type='A' or @type='B'] • the previouschaptersibling: preceding-sibling::chapter[1] 4: Overview of XSLT

  36. Location path examples (2) • All child elements having an attributetype: *[@type] NB: Node sets as truth values: empty - false; non-empty - true • All child elements of any author child: author/* • sections whosetype attribute equals styleattribute of the document element: //sect[@type = /*/@style] • First authorchild, and previous to the last: author[1], author[last()-1] 4: Overview of XSLT

  37. Main Aspects of XSLT • Data model • Selection mechanism • Matching • How are the rules selected? • A: With Patterns • Processing model 4: Overview of XSLT

  38. XSLT Patterns • Main use in match attributes of template rules: <xsl:template match="Pattern"> • also used for numbering (Which parts are counted?) • Restricted location path expressions: • steps with childand attributeaxes only, separated by '//' or '/' • but arbitrary predicates in [Expr]allowed • may begin withid('IdVal')(for selecting element nodes by ID attribute values) • alternative patterns separated by '|' (~ node-set union) 4: Overview of XSLT

  39. XSLT Patterns: Semantics • A node n matches a pattern P if n would be selected by P in some context • > the context has to be an ancestor of n • can be tested by considering Steps of P right-to-left and checking that they can be satisfied along a path from n towards root 4: Overview of XSLT

  40. XSLT Patterns: Examples • match="sect-head | section/head" • matches any element with namesect-head, and anyheadelements directly below asection • Pattern/appendix//ulist/item[1]matches the first itemelement in aulistwhich is contained in anappendix, which is the document element 4: Overview of XSLT

  41. Main Aspects of XSLT • Data model • Selection mechanism • Matching • Processing model • How does the XSLT execution proceed? 4: Overview of XSLT

  42. XSLT Processing Model 0. Parse the document into a source tree 1. Construct the result tree by applying template rules to the source tree 2. Serialize the result tree (as XML, HTML or text) 4: Overview of XSLT

  43. Overview of XSLT Transformation 4: Overview of XSLT

  44. XSLT Result Construction Algorithm (sketch) ResultTree:= ApplTempls([root of the source tree]); procApplTempls(CNL: list of Nodes) returns list of Nodes: ResList:= emptyNodeList(); for each Node cnin CNL do // current node in current node list Find matching template rule (of highest priority; See next) Instantiate its template T in context (cn, CNL), and add to ResList; Replace each <apply-templates select="E"/> in T by ApplTempls(L), where L = value of expr E in context (cn, CNL); end for; returnResList; Example: seenext 4: Overview of XSLT

  45. Rules:<xsl:templatematch="/"> <X> <xsl:apply-templatesselect="A/B" /> </X></xsl:template><xsl:templatematch="B"> <Y pos="{position()}"> <xsl:apply-templates /> </Y></xsl:template> <xsl:templatematch="C"> <Z pos="{position()}"> <xsl:apply-templates /> </Z></xsl:template> • Source: <A><B><C /></B><B><C /></B></A> • Result: 4: Overview of XSLT

  46. Selecting one of matching rules • Priority of a rule can be specified explicitly: <xsl:template priority="2.0" … • Default priorities based on the match pattern: • 0 for simple name tests (likepara, @href) • negative for less specific patterns e.g., *, @*, node() • 0.5 for more complex patterns • Multiple matching rules with the same maximum priority is an error - Processor may (quietly!) choose the last one of them 4: Overview of XSLT

  47. Application of template rules • Without a selectattribute <xsl:apply-templates />processes all children of current node ~ select="child::node()")  “default traversal”: top-down • Nodes are processed in document order (if not sorted with xsl:sort) • Built-in rules support the top-down traversal if no matching rules are found 4: Overview of XSLT

  48. Built-In Default Rules • For the root and element nodes:<xsl:template match="/ | *"> <xsl:apply-templates /> </xsl:template> • For text and attribute nodes:<xsl:template match="text() | @*"> <!-- Insert the string value of current node: --> <xsl:value-of select="." /> </xsl:template> • Low priority->can be overridden 4: Overview of XSLT

  49. A (Tricky) Processing Example • Consider transforming document <A><B>b1</B><C>cc<B>b2</B></C><D>dd</D><B>b3</B></A> with the below rules: <xsl:template match="/"> <!-- Rule 1 --> <R><xsl:apply-templates select="//C" /></R> </xsl:template> <xsl:template match="C"> <!-- Rule 2 --> <NewC>New: <xsl:apply-templates select="../B" /> <xsl:apply-templates /> </NewC> </xsl:template> 4: Overview of XSLT

  50. Processing example (2) • The result <R><NewC>New: b1b3ccb2</NewC></R> is obtained as follows: 1. Rule 1 matches the root node -> Element node R is added to the result; Instruction <xsl:apply-templates select="//C" />selects the (only)Celement for processing (which will produce the contents of node R). 2. Rule 2 with pattern"C"creates into result tree aNewCelement node with text node "New: "as its first child. 4: Overview of XSLT

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