Learning XSLT

Learning XSLT A Tutorial Mike Fitzgerald Wy’east Communications

Quick Start: What Is XSLT? Extensible Stylesheet Language or XSLT XML Path Language or XPath is a companion specification to XSLT Both recommendations published by the World Wide Web Consortium (W3C) in November 1999

Quick Start: Templates XSLT stylesheets are driven by templates Documents processed on a template model Templates can have: (1) innate priority or (2) assigned assigned priority (rare) Templates can have modes Can name templates, pass them parameters Built-in templates Attribute value templates

Quick Start: XPath XPath is a non-XML syntax for addressing nodes with location paths XPath data model describes XML documents with seven node types Types are root (document in 2.0), element, attribute, text, namespace, comment, processing instruction

Quick Start: More XPath Expressions in attribute values Patterns, subset of expressions Predicates, method for filtering nodes Axes, forward and reverse Arithmetic in expressions Functions in expressions (XSLT adds functions XPath set of functions)

Quick Start: Output Output methods: text, XML, or HTML (XHTML in 2.0) Literal result elements Instruction elements Control over things like indentation, XML declarations, document type declarations, media types, and more

Quick Start: Processing Several methods of copying nodes across Variables and parameters Can pass parameters in from outside stylesheet, and outside a template Can process nodes conditionally Sorting and numbering of lists

Quick Start: Keys Keys are mainly a performance hike You can use more than one key You can use parameters with keys You can cross-reference with keys

Quick Start: Multiple Documents Multiple stylesheets through inclusion Multiple stylesheets through importation Multiple source documents Multiple output documents (through extension in 1.0, standard in 2.0)

Quick Start: Alternative Stylesheets Normal stylesheets Literal result stylesheets Embedding stylesheets Namespace aliasing Namespace exclusion

Quick Start: Extensions XSLT designed for extension Can use processor-specific extensions, such as those from Xalan, Saxon, EXSLT Can extend XSLT yourself XSLT 2.0 provides a native way to write extension functions in XML syntax

Main Presentation A brief introduction to XSLT and XPath Focus on version 1.0, with asides to 2.0 Most features covered, though not all Basic understanding of XML assumed Example files available on CD (in DOS format, so use conv –U for Unix line endings)

W3C Specifications XSLT 1.0 specification http://www.w3.org/TR/xslt XPath 1.0 specification http://www.w3.org/TR/xpath Working drafts of version 2.0 editions http://www.w3.org/TR/xslt20 http://www.w3.org/TR/xpath20

What Is XSL-FO? Originally, XSLT was included in Extensible Stylesheet Language or XSL XSL deals with appearance, formatting XSL is commonly called XSL-FO Specs parted company in April 1999

What Does XSLT Do? A language in XML syntax that defines and describes transformations Transforms XML to: XML HTML XHTML (2.0) plain text

From Source to Result Source XML document becomes source tree Source document could be a file or a stream Result document could be a file or stream A result tree can be serialized as an XML, XHTML, HTML, or text document Text documents could be C++, Java, Python, SQL, or what have you

Process Flow Source Style- sheet Result Processor Inputs Processor Output

Templates The template is the heart of XSLT Templates match patterns in source trees A pattern is generally a location in the structure of the source tree A template is invoked to search for a pattern A template that finds a pattern can be instantiated and create a result tree for output

Stylesheet Basics A document element in XSLT can be stylesheet or transform version is required attribute Namespace declaration is required http://www.w3.org/1999/XSL/Transform Conventional prefix is xsl

ch01/msg.xml & ch01/msg.xsl ch01/msg.xml just an empty document element ch01/msg.xsl , document element is stylesheet , version attribute, namespace Top-level element output , and method attribute with value of text Top-level element template matches the pattern msg using the match attribute Literal result text Found it!

Some XSLT Processors Instant Saxon ( http://saxon.sourceforge.net ) saxon msg.xml msg.xsl Saxon ( http://saxon.sourceforge.net ): java –jar saxon7.jar msg.xml msg.xsl Xalan C++ ( http://xml.apache.org ): xalan msg.xml msg.xsl XRay ( http://www.architag.com ) xmlspy ( http://www.xmlspy.com )

A Simple Transformation Transform the document with the stylesheet: xalan msg.xml msg.xsl Yields this result: Found it! How did that happen?

ch01/msg-pi.xml An XML stylesheet processing instruction is similar to the HTML element LINK Points to a stylesheet: <?xml-stylesheet href= " msg.xsl " type= " text/xsl " ?> Some processors accept text/xslt A W3C specification: http://www.w3.org/TR/xml-stylesheet

XSLT & Browsers Several browsers support client-side XSLT transformations, such as IE 6.0, Netscape 7.1, Mozilla 1.7, Firebird 0.9 Load ch01/msg-pi.xml in a browser See the results in that browser

ch01/message.xml XML declaration with version information An XML declaration is not a processing instruction Document element message Attribute priority with value low Text content (#PCDATA in DTD terms)

value-of Instruction Element Children of top-level elements are usually instruction elements value-of ’s required select attribute Returns a string value

ch01/message.xsl stylesheet element with version and namespace output element, method is text template matches message value-of selects text content of message text() is a node test for text nodes

Another Transformation Transform the document with the stylesheet: xalan message.xml message.xsl Yields this result: Hey, XSLT isn’t so hard after all! What happened?

Applying Templates Templates processes children of the matched node The apply-templates finds other templates that match those children The select attribute of apply-templates finds a specific template that matches a child

XPath 1.0 Data Model XPath sees XML documents as a set of one or more nodes of seven types: Root (or document in 2.0) Element Attribute Text Namespace Comment Processing instruction

ch04/nodes.xml via ch04/tree-view.xsl

Root Node The root node is the root of the XML document Called the document node in XPath 2.0 Has at most one element node child, that is, the root or document element Location path: /

Element Nodes Elements are the building blocks of structured XML documents A location path: message/body/line All elements: * All elements of a given namespace (name test): rng:*

Attribute Nodes Attributes effectively modify elements Location path: message/@priority All attributes: @* xmlns , with or without a prefix (as in xmlns:rng ), is not treated as an normal attribute

Other Nodes Match text nodes with text() node test Match namespace nodes with namespace::* axis or namespace-uri() function Match comments with comment() node test Match processing instructions with processing-instruction() node test

Built-in Template Rules Hidden magic that is sometimes confusing Automatically kick in when an explicit matching template is not found, but a node matching the built-in template is present In absence of appropriate templates, built-in templates are used

Built-in Templates... Match patterns Match the root node and all element nodes, including modes Match text and attributes No-ops on comments, processing instructions, namespace nodes Try ch10/built-in.xsl

Template Rules Templates have priority when more than one template matches the same node The template element has a priority attribute which takes a real number Stylesheets can be included and imported Imported templates are governed by import precedence rules

Literal Result Elements You can literally add text, elements, and attributes to a result tree Can use attribute value templates ( {} ) in the attribute values of literal result elements Namespaces apply to literal result elements Markup in stylesheet subject to well-formedness constraints

Literal Examples Examples from ch02 ... Literal text: xalan text.xml txt.xsl Literal result element: xalan literal.xml literal.xsl Literal HTML markup: xalan literal.xml html.xsl Literal XHTML markup (with 1.0): xalan doc.xml doc.xsl

Instruction Elements element creates an element attribute creates an attribute attribute-set creates a reusable set of attributes (top-level element) text creates text comment creates comments processing-instruction creates a PI

ch02/final.xsl attribute-set is a top-level element that can contain zero or more attribute elements processing-instruction creates an XML stylesheet PI for a CSS document comment adds a comment to the document prolog before document element

More on ch02/final.xsl Literal result elements element creates elements attribute value is derived the from source using an absolute location path text element adds some text to the result without adding unintended whitespace

output Element Top-level element (zero or more) Controls output methods: xml , html , text or a QName (qualified name) xhtml method available in XSLT 2.0 Structural indentation with the indent attribute ( yes or no ) encoding attribute has values such as US-ASCII , UTF-8 , or ISO-8859-1

XML Declaration & output omit-xml-declaration attribute ( yes or no ) version attribute sets version information standalone attribute sets standalone declaration ( yes or no )

More on output media-type attribute sets media type as in text/xml or application/xml cdata-section-elements sets result tree elements that contain CDATA sections doctype-system and doctype-public output document type declarations using SYSTEM or PUBLIC identifiers See examples in ch03

Expressions Defined by XPath Expressions in select attributes Expressions can contain: patterns (next slide) boolean and relational logic ( and , or , != , > ) arithmetic ( + , - , * , / , mod ) functions ( name() , last(), count()) variable references ( $var )

Patterns Defined by XSLT as subset of an expression Patterns most often in match attributes Patterns often contain: location steps ( date/year ) / (root) or // (descendant) or | (union) Node test ( * , rng:* , comment() , text() ) id() or key() functions child:: or attribute:: axes Predicate ( state/name[.='Oregon'] )

Axes Abbreviated and unabbreviated syntax Double colon separator ( attribute::priority ) Forward or reverse axes: Forward: attribute, child, descendant, descendant-or-self, following, following-sibling, namespace, parent, self Reverse: ancestor, ancestor-or-self, preceding, and preceding-sibling See examples in ch04

Functions Part of expressions, so always called in attribute values that contain expressions (usually select ) Node-set, number, boolean, string functions XPath functions examples: position() , concat() , not() , sum() XSLT function examples: document() , current() , key() , format-number() See examples in ch05

Copying Nodes Shallow copy versus deep copy copy element performs a shallow copy: element nodes and namespace nodes copy-of element performs deep copy: element and child nodes, attribute nodes, namespace nodes See examples in ch06

Variables & Parameters variable and param elements, both top-level or instruction elements Referenceable value ( $var ) with scope Can’t change variable value Result tree fragment or temporary tree in XSLT 2.0 (see with extensions) See examples in ch07

More on Variables & Parameters param value can change, have default Can pass parameters to a stylesheet Can pass parameters to a template using with-param

Sorting Nodes The sort element sorts nodes Child of apply-templates or for-each Ascending or descending Alphabetical or numerical If alphabetical, by uppercase or lowercase See examples in ch08

Numbering Nodes The number element inserts formatted numbers into result tree as for a list Numerical, alphabetical, Roman numerals Used with format-number() function Also used with decimal-format top-level element See examples in ch09

Named Templates A template element can have a name attribute Can have match and name attributes together, but if no match , must have name Can call templates by name with the call-template element, with parameters ( with-param ) Displaced by XSLT 2.0 element function See examples in ch10

Modes Can’t apply template that matches a given node more than once Overcome by modes Matching mode attribute on template and apply-templates

Keys Can match nodes based on a key value Define keys at the top-level using the key element Later called using the key() function in patterns or expressions See examples in ch11

Conditional Processing Test a single condition with an expression using an if instruction element Test multiple conditions with expressions using when instruction elements in choose (if-then statement) choose can contain optional otherwise element (if-then-else statement) See examples in ch12

Including Stylesheets Can include external stylesheet(s) with include element Include effectively merges stylesheets See examples in ch13

Importing Stylesheets Can also import external stylesheet(s) with import element Import builds import tree with precedence based on sequence of imports apply-imports can trump normal precedence See examples in ch13

Alternative Stylesheets Literal result element stylesheet uses a literal result element as the document element Embedded stylesheets allow you to combine source tree and stylesheet into one document by using a fragment identifier with an id attribute See examples in ch14

Extensions XSLT 1.0 can’t satisfy everyone, so extensions possible Can write namespace-qualified extension elements, functions, and attributes Can define your own extensions or use extensions already defined Can define fallback behavior using fallback and message elements See examples in ch15

XSLT 2.0 Highlights xhtml output method Multiple result trees ( result-document ) Regular expressions ( analyze-string ) Define stylesheet functions ( function ) Validation with XML Schema Format dates ( date-format , format-date() ) Grouping ( for-each-group ) Character maps ( character-map , output-character )

XPath 2.0 Highlights Many new functions (177 versus 27) Strongly typed, relying on XML Schema datatypes Kind tests ( document-node() , element(), attribute() ) Casting ( cast , castable ) for and if statements in expressions See examples in ch16

Ox Documentation Tool Syntax-related XSLT documentation on the command line XML vocabulary items, too Example: java –jar ox.jar xsl:text See: http://www.wyeast.net/ox.html

So Long and Thanks! Mike Fitzgerald Wy’east Communications

Learning XSLT

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Learning XSLT