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XSLT

Explore XSLT language components, rules, and applications for transforming XML to HTML effortlessly. Learn with experts from Florida State University.

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XSLT

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  1. XSLT Instructors: Geoffrey Fox and Bryan Carpenter Dept. of Computer Science School of Computational Science and Information Technology 400 Dirac Science LibraryFlorida State UniversityTallahassee Florida 32306-4120 http://www.csit.fsu.edu Nancy McCracken, Ozgur Balsoy http://aspen.csit.fsu.edu/webtech/xml/ it2xslt http://aspen.csit.fsu.edu/it2spring01

  2. XSL Transformations • XSL is the Extensible Style Language. • It has two parts: the transformation language and the formatting language. • In this lecture we are concerned with XSL transformations, or XSLT. • The formatting language will be discussed later. • XSLT provides a syntax for defining rules that transform an XML document to another document. • For example, to an HTML document. • An XSLT “style sheet” consists primarily of a set of template rules that are used to transform nodes matching some patterns. it2xslt http://aspen.csit.fsu.edu/it2spring01

  3. Transforming XML • Consider the important application of transforming an XML document to HTML, for display purposes. • This could happen in various places: • In a Web server. A servlet might convert XML documents stored on the server to HTML documents that are sent to the client via HTTP. • In a Web browser. An XSL-enabled browser may convert XML downloaded from the server to HTML, prior to display. Currently Internet Explorer supports a subset of XSLT. • In a standalone program. XML stored in or generated from a database, say, may be “manually” converted to HTML before placing it in the server’s document directory. • In any case, a suitable program takes an XML document as input, together with an XSLT “style-sheet”. it2xslt http://aspen.csit.fsu.edu/it2spring01

  4. Example • Here is an XML source file that includes a “stylesheet” declaration: <?xml-stylesheet type="text/xsl" href="emptable.xsl" version="1.0"?> <EMPLOYEE> <PERSON> <EMPNO>100</EMPNO> <ENAME>JAMES </ENAME> <JOB>PRESIDENT</JOB> </PERSON> <PERSON> <EMPNO>201</EMPNO> <ENAME>KELLY </ENAME> <JOB>CLERK</JOB> </PERSON> . . . </EMPLOYEE> it2xslt http://aspen.csit.fsu.edu/it2spring01

  5. Style sheet emptable.xsl <?xml version="1.0" ?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/TR/WD-xsl"> <xsl:template match="/"> <HTML> <BODY> <TABLE WIDTH="100%" ALIGN="center" BORDER="1"> <TR> <TH>Number</TH> <TH>Name</TH> <TH>Job</TH> </TR> <xsl:for-each select="EMPLOYEE/PERSON"> <TR> <TD> <xsl:value-of select="EMPNO" /> </TD> <TD> <xsl:value-of select="ENAME" /> </TD> <TD> <xsl:value-of select="JOB" /> </TD> </TR> </xsl:for-each> </TABLE> </BODY> </HTML> </xsl:template> </xsl:stylesheet> it2xslt http://aspen.csit.fsu.edu/it2spring01

  6. Remarks • The xml-stylesheet element in the XML instance references an XSL style sheet. • In general, children of the stylesheet element in a stylesheet are templates. • A template specifies a pattern; the template is applied to nodes in the XML source document that match this pattern. • In this example the only pattern is trivial: the pattern “/” matches the root node of the document. • In the transformed document, the body of the template element replaces the matched node in the source document. • In addition to text, the body may contain further XSL terms, e.g.: • xsl:foreach repeats the enclosing template text for each member of a selected set of sub-nodes. • xsl:value-of extracts data from selected sub-nodes. it2xslt http://aspen.csit.fsu.edu/it2spring01

  7. Viewing the example with Internet Explorer it2xslt http://aspen.csit.fsu.edu/it2spring01

  8. References • Inside XML, Chapter 13: “XSL Transformations”. • “XSL Transformations (XSLT)”, version 1.0: http://www.w3.org/TR/xslt • “XML Path Language (XPath)”, version 1.0: http://www.w3.org/TR/xpath it2xslt http://aspen.csit.fsu.edu/it2spring01

  9. Xpath it2xslt http://aspen.csit.fsu.edu/it2spring01

  10. XML Path Language • The XML Path Language, or Xpath, is a language for addressing parts of an XML document. • It is an essential part of XSLT, and also Xpointer (as well as being used in XML schema). • The patterns and other node selections appearing in XSLT rules are represented using Xpath syntax. • Including the match element of xsl:template or the select element of xsl:value-of. • In simple cases an Xpath expression looks like a UNIX path name, with nested directory names replaced by nested element names: • “/” is the root element of a document • expressions may be absolute (relative to the root) or relative to some context node. it2xslt http://aspen.csit.fsu.edu/it2spring01

  11. Types of Xpath expressions • Xpath expressions evaluate to one of four possible types of thing: • A node-set: a collection of nodes in the XML document. See below for the description of “node”. • A boolean value: true or false. • A number: always represented internally as a double-precision floating point, although they may be written and used as an integer. • A string. • The nodes that can appear in a node-set include: • element nodes and attribute nodes, • text nodes (plain text children of some element), and also • root nodes, namespace nodes, processing instruction nodes and comment nodes. • In the end we are interested in Xpath expressions that evaluate to a node-set, although other expression types will appear. it2xslt http://aspen.csit.fsu.edu/it2spring01

  12. Location paths • The most important kind of Xpath expression—the one that gives Xpath its name—is the location path. • In general a location path consists of a series of location steps separated by the slash “/”. • As noted earlier, the commonest example of a location step—analogous to a UNIX directory name—is an XML element name. • Actually this common case is an example of what is called abbreviated syntax. • To be systematic, we will describe the general, unabbreviated syntax for location paths first. it2xslt http://aspen.csit.fsu.edu/it2spring01

  13. Parts of a location step • An individual location step has three logical parts: • The axis—a keyword which, loosely speaking, describes the “dimension” this location step takes us into. • Simple examples are child and attribute which, respectively, say that this step enters the set of children or the set of attributes of an element. • A node test—this is typically an element or attribute name, selecting within the chosen axis. It may also, less specifically, be a node type. • Zero or more predicates, which use arbitrary Xpath expressions to further refine the set of selected nodes. • The unabbreviated syntax for a location step is: axis :: node-test [predicate1] [predicate2] . . . it2xslt http://aspen.csit.fsu.edu/it2spring01

  14. Axes • Any location step starts from some context node; the axis is relative to this node. • The available axes are: • child—contains the children of the context node. • descendent—contains children and all descendents of children. • parent—contains the parent of the context node. • ancestor—contains parent and ancestors of parent. • attribute—contains the attributes of the context node. • following—all following element nodes, in document order. • preceding—all preceding element nodes, in document order. • following-sibling, preceding-sibling—elements at the same syntactic level. • namespace—containsnamespace nodesof context node. • self, descendent-or-self,ancestor-or-self it2xslt http://aspen.csit.fsu.edu/it2spring01

  15. The NodeTest • After choosing the axis, we refine the selection with a node test. • The most common cases for a the node-test field are likely to be: • an element or attribute name, selecting nodes in the axis with the given name, or • the wildcard, “*”, selecting all nodes of the “principal type” for this axis (typically, all element nodes, or all attribute nodes if axis is attribute). • The node-test field may also be a node type expression: • comment(), text(), processing-instruction(), node() • Optionally, theprocessing-instruction()function may include a literal string specifying a particular type of instruction. it2xslt http://aspen.csit.fsu.edu/it2spring01

  16. Predicates • The node test is optionally followed by a series of predicate expressions. • Each expression appears in []s. • Syntax of the expressions will be briefly discussed later. Some examples appear in the next few slides. • The predicates are computed successively to further filter the set of selected nodes—after each predicate is applied, the selected node set is reduced to exclude those elements for which the expression evaluates to false. • Following examples are taken from the XML Path Language specification. it2xslt http://aspen.csit.fsu.edu/it2spring01

  17. Example location paths child :: para • para element children of the context node child :: * • All element children of the context node child :: text() • All text node children of the context node child :: node() • All children, regardless of node type attribute :: name • The name attribute of the context node attribute :: * • All attributes of the context node decendent :: para • para element descendents of the context node ancestor :: div • div element ancestors of the context node it2xslt http://aspen.csit.fsu.edu/it2spring01

  18. More complex examples child :: chapter/descendent :: para • para element descendents of chapter element children of the context node. child :: */child :: para • All para element grandchildren of the context node. /descendent :: para • All para elements in this document. child :: para [position() = 1] • First para element child of the context node. child :: para [position() = last()] • Last para element child of the context node. child :: para [position() > 1] • All para element children of the context node, except the first. /child :: doc/child :: chapter [position() = 5]/child :: section • section elements of 5th chapter element of root doc element. child :: para [attribute :: type = ‘warning’] [position() = 5] • 5th para child of context node having type attribute value “warning”. it2xslt http://aspen.csit.fsu.edu/it2spring01

  19. Predicate expressions • The axis in a location step defines a node-set, which is then filtered by the node test to produce a reduced node set. • A predicate is evaluated for each element of the node set selected so far: • The context node for the predicate expression is the element being filtered (not the context node for the location step as a whole!) • The context set for the predicate expression is the node set currently being filtered. it2xslt http://aspen.csit.fsu.edu/it2spring01

  20. Context Position • Various functions are available in Xpath expressions, e.g.: • last() returns the size of the context set for the expression. • position(): the position of the context node in the context set. • If the Xpath expression that appears in the predicate of a path step evaluates to numeric type, it is converted to true if its value is equal to position(). • Otherwise it is converted to false. • Thus, by definition, the location step: child :: para [5] is an alternative to: child :: para [position() = 5] i.e.,the 5th para child. it2xslt http://aspen.csit.fsu.edu/it2spring01

  21. Booleans • In general an Xpath expression is converted to a boolean—if context demands—by the following rules: • A non-zero number converts to true, zero converts to false. • A non-empty string converts to true true, empty to false. • A non-empty node converts to true, empty to false. • According to the third rule, in the location step: child :: section [child :: para] the predicate is true if the context node for the predicate (i.e. the section node) has at least one para child. • Operators and, or, not() are available. it2xslt http://aspen.csit.fsu.edu/it2spring01

  22. Comparisons • Numeric and string comparisons in Xpath predicates follows obvious rules. • Comparisons involving node sets are defined to be true if the comparison would hold true for the string-valueof any elements of the sets involved. • Note, the string value of an element node is a concatenation of the string values of its children. • For example, in child :: para [attribute :: type = ‘warning’] the predicate is true iff the node set attribute :: type includes an element with string-value “warning”, i.e. if the para child has an attribute with value “warning”. it2xslt http://aspen.csit.fsu.edu/it2spring01

  23. Unions • The operator “|” forms the union of two node sets. • e.g. child :: chapter [child :: section | child :: para] selects chapters that directly contain a section or a para. it2xslt http://aspen.csit.fsu.edu/it2spring01

  24. Abbreviated syntax for paths • Together, the following abbreviations allow the UNIX-like path syntax seen earlier: • The axis selector child :: can always be omitted: a node test alone implicitly refers to the child axis. • The location step “.” is short for self :: node(). • The location step “..” is short for parent :: node(). • Other useful abbreviations are: • The axis selector attribute :: can be abbreviated to @. • // is short for /descendent-or-self :: node()/ • e.g //para is short for any para element in the document. it2xslt http://aspen.csit.fsu.edu/it2spring01

  25. XSLT it2xslt http://aspen.csit.fsu.edu/it2spring01

  26. Format of a Style Sheet • Of course an XSLT style sheet is itself an XML document. • In this lecture we will be using the XSLT elements from the namespace http://www.w3.org/1999/XSL/Transform. • As a matter of convention we use the prefix xsl: for this namespace. • The document root in an XSLT style sheet is an xsl:stylesheet element, e.g.: <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" > . . . </xsl:stylesheet> • A synonym for xsl:stylesheetisxsl:transform. • Several kinds of element can be nested inside xsl:stylesheet, but by far the most important is the xsl:template element. it2xslt http://aspen.csit.fsu.edu/it2spring01

  27. The xsl:template element • The xsl:template element has a few possible attributes, but the only one we will consider is the match attribute, which is generally required • unless this template element is a reference to an actual template defined elsewhere. • So all our templates will have the form: <xsl:template match=“pattern”> template body </xsl:template> • The pattern is an Xpath expression describing the nodes to which the template can be applied. • The processor scans the input document for nodes matching this pattern, and replaces them with the text included in the template body. • In a nutshell, this explains the whole operation of XSLT. it2xslt http://aspen.csit.fsu.edu/it2spring01

  28. Patterns • The value of the match attribute is a (slightly restricted) Xpath expression. • The expression must evaluate to a node set, and the top-level of the expression should normally be a location path. • A few other cases allowed, e.g. unions of location paths. • Arbitrary Xpath expressions can appear nested in predicates. • Location steps in the top-level location paths may only use the child or attribute axes. • The unabbreviated descendant axis cannot be used, but the special case syntax //is allowed. it2xslt http://aspen.csit.fsu.edu/it2spring01

  29. Matching patterns • Formally: a pattern is defined to match a node iff the node has an ancestor node such that evaluating the Xpath expression with the ancestor as context gives a node set that contains the node. • In practice the rules are easy to understand, e.g.: para • Matches all para elements in the search space. text() • Matches all text nodes in the search space. @name • All name attributes of all elements in the search space. para [position() = 1] • All para elements that are first children of their parent element. chapter [5]//section • All section elements in all chapter elements in position 5. it2xslt http://aspen.csit.fsu.edu/it2spring01

  30. The template body • When a node is matched, the body of the xsl:template element is evaluated, and the resulting text placed in the output document. • The template body may include plain text, which is copied straight to the output document. • It may also include nest XSLT elements that need to be further processed. • These will be evaluated in the context of the matched node. • Important examples of XSLT elements that may appear in the body of a template: • The xsl:value-of element. • The xsl:apply-templates element. • The xsl:element and xsl:attribute elements. • More “procedural” elements, like xsl:for-each, xsl:if. it2xslt http://aspen.csit.fsu.edu/it2spring01

  31. An input document <?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet type="text/xml" href="eg.xsl"?> <planets> <planet> <name>Mercury</name> <mass>0.0553</mass> <day units="days">58.65</day> <radius units="miles">1516</radius> <density>0.983</density> </planet> <planet> <name>Venus</name> <mass>0.815</mass> <day units="days">116.75</day> <radius units="miles">3716</radius> <density>0.943</density> </planet> <planet> <name>Earth</name> <mass>1</mass> <day units="days">1</day> <radius units="miles">2107</radius> <density>1</density> </planet> </planets> Simplified version of example from the “Inside XML” book (complete with astronomical errors). it2xslt http://aspen.csit.fsu.edu/it2spring01

  32. Using an empty style sheet • Consider the example where there are no templates explicitly specified, eg.xsl has the form: <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" > </xsl:stylesheet> • The transformation of the input document is: Mercury0.055358.6515160.983Venus0.815116.7537160.943Earth1121071 i.e. just the concatenated string values in all text nodes. • This happens because there is a default template rule: <xsl:template match=“text()”> <xsl:value-of select=“.”/> </xsl:template> it2xslt http://aspen.csit.fsu.edu/it2spring01

  33. Templates without embedded XSLT • Now consider a single template, with no embedded XSLT commands: <?xml version="1.0" encoding="UTF-8"?> <xsl:stylesheet version="1.0” xmlns:xsl="http://www.w3.org/1999/XSL/Transform" > <xsl:template match="planet"> <p>planet discovered</p> </xsl:template> </xsl:stylesheet> • The transformation of the input document is: <?xml version="1.0" encoding="UTF-16"?><p>planet discovered</p><p>planet discovered</p><p>planet discovered</p> This is valid HTML, but not very readable (as text). • We can add the command: <xsl:output indent="yes"/> to the xsl:stylesheet element to get prettier output formatting. it2xslt http://aspen.csit.fsu.edu/it2spring01

  34. The xsl:apply-templates element • Suppose a second template matching the planets element is added: <xsl:template match="planet"> <p>planet discovered</p> </xsl:template> <xsl:template match="planets"> <h1>All Known Planets</h1> </xsl:template> • The output now only contains the header: <h1>All Known Planets</h1> not the “planet discovered” messages from processing the nested planet elements. • Once a match is found, nested elements are not processed unless there is an explicit <xsl:apply-templates> instruction: <xsl:template match="planets"> <h1>All Known Planets</h1> <xsl:apply-templates/> </xsl:template> it2xslt http://aspen.csit.fsu.edu/it2spring01

  35. The xsl:value-of element • We can now match arbitrary nodes in the source document, but we don’t yet have a way to extract data from those nodes. • To do this we need the xsl:value-of element, e.g.: <xsl:template match="planet"> <p>planet <xsl:value-of select="name"/> discovered</p> </xsl:template> <xsl:template match="planets"> <h1>All Known Planets</h1> <xsl:apply-templates/> </xsl:template> • We now get the more interesting output: <h1>All Known Planets</h1> <p>planet Mercury discovered</p> <p>planet Venus discovered</p> <p>planet Earth discovered</p> it2xslt http://aspen.csit.fsu.edu/it2spring01

  36. Selections • The select attribute of the xsl:value-of element is a general Xpath expression. • Its result—which may be a node set or other allowed value—is converted to a string and included in the output. • For example, the selection can be an attribute node, a set of elements, or it could be the result of a numeric computation. • If the selection is a set of elements, the text contents of all the element bodies, including nested elements, are concatenated and returned as the value. it2xslt http://aspen.csit.fsu.edu/it2spring01

  37. Xpath expressions in attributes • Suppose we want to generate an XML element in the output with an attribute whose value is computed from source data. • One might be tempted to try a template like: <planet name = "<xsl:value-of select='name'/>" > Status: discovered </planet> • This is ill-formed XML: we cannot have an XML element as an attribute value. • Instead {}s can be used in an attribute value to surround an Xpath expression: <planet name = "{name}" > Status: discovered </planet> • The Xpath expression name is evaluated exactly as for a select attribute, and interpolated into the attribute value string. it2xslt http://aspen.csit.fsu.edu/it2spring01

  38. The xsl:element element • For similar reasons we cannot use <xsl:value-of> to compute an expression that is used as the name of an element in the generated file. • Instead one can use instead the xsl:element element. • These can optionally include nested xsl:attribute elements (as their first children): <xsl:template match="planet"> <xsl:element name="{name}"> <xsl:attribute name="distance"> <xsl:value-of select="distance"/> </xsl:attribute> Status: discovered </xsl:element> </xsl:template> • When this template matches a planet, it generates an XML element whose name is the planet, with a distance attribute. it2xslt http://aspen.csit.fsu.edu/it2spring01

  39. A Table of Planets <xsl:template match="planets"> <html><body> <h1>All Known Planets</h1> <table width="100%" align="center" border="1"> <tr><th>name</th><th>mass</th><th>density</th> <th>radius</th></tr> <xsl:apply-templates/> <!-- rows of table --> <tr> <td>AVERAGES</td> <td> <xsl:value-of select="sum(planet/density) div count(planet)"/> </td> <td></td> <td></td> </tr> </table> </body></html> </xsl:template> it2xslt http://aspen.csit.fsu.edu/it2spring01

  40. A row of the table <xsl:template match="planet"> <tr> <td><xsl:value-of select="name"/></td> <td><xsl:value-of select="mass"/></td> <td><xsl:value-of select="density"/></td> <td><xsl:value-of select="radius"/></td> </tr> </xsl:template> it2xslt http://aspen.csit.fsu.edu/it2spring01

  41. The display it2xslt http://aspen.csit.fsu.edu/it2spring01

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