XML - XSLT © 2012 t he University of Greenwich 1 XML Processing with XSLT Kevin McManus

XML - XSLT © 2012 t he University of Greenwich 2 Namespaces Namespaces are a way of avoiding name conflicts, i.e. where different XML vocabularies use the same names to mean different things. In designing an XML based language we may want to include elements from several other XML languages e.g. ProductMLCustomerML InvoiceML when defining a new XML language to describe invoice documents we may want to draw on existing languages for describing products and customers

XML - XSLT © 2012 t he University of Greenwich 3 Namespaces What to do about name clashes, e.g. it is likely that ProductML and CustomerML both contain elements Giant Widget George Barford We don't want applications that process InvoiceML to confuse the elements. Dear Mr Giant Widget, Your George Barford has been despatched today...

XML - XSLT © 2012 t he University of Greenwich 4 Namespaces Namespaces give a mechanism for "qualifying" element names with a prefix so that they are all unique, e.g. Giant Widget George Barford Wherever you see element names including a prefix followed by a ":" you can be sure that namespaces are being used e.g.

XML - XSLT © 2012 t he University of Greenwich 5 Namespaces The prefix needs to be defined in the XML document that is using it by including the xmlns attribute. For example to define the prod: and cust: prefixes in an invoice document declaring a default namespace that uses no prefix <invoices xmlns:prod=" xmlns:cust=" xmlns=" Giant Widget George Barford.... declaring a namespace associated with the prod prefix declaring a namespace associated with the cust prefix

XML - XSLT © 2012 t he University of Greenwich 6 Namespaces In the previous example it is tempting to guess that this line… <invoices xmlns:prod=" xmlns:cust=" xmlns=" associates the prod: prefix with an XML Schema located at and cust: with one at But these URLs need not be actual locations at all - they are simply unique names used to identify namespaces. URIs (URLs & URNs) are convenient ways of specifying unique values. There is a way of tying prefixes to actual XML Schemas (but not DTDs) so that documents can be validated against multiple Schemas. The syntax is both messy and unclear and beyond what we are going to look at here.

XML - XSLT © 2012 t he University of Greenwich 7 The need for style sheets with XML XML defined tags describe document content but not presentation Presentation information can be added using of style sheets. XML document + style sheet = presentable document There are two main style sheet languages - both are W3C standards –CSS - Cascading Style Sheets –XSL - eXtensible Stylesheet Language (XML Stylesheet Language) CSS is a more mature (in Internet terms) standard XSL itself consists of two languages –XSL Transformations (XSLT) can restructure an XML document - often used to convert XML into HTML or XHTML –XSL Formatting Objects (XSL-FO) defines how elements are displayed. XSLT and XSL-FO can be used independently XSL-FO has some opponents XSLT is more stable and widely used and is what is covered here.

XML - XSLT The difference between CSS and XSL XSLT XSL-FO or CSS CSS Spot the difference? plain XML XML rendered XML transformed XML transformed and rendered XSL - can restructure an XML document and then format it for display

XML - XSLT © 2012 t he University of Greenwich 9 XSLT is a transformation language XSLT is very different from CSS XSLT can transform an XML document into any other format (e.g. another XML document, HTML, PDF, plain text). For display in a browser it makes sense for the output document to be in HTML or XHTML format because that is what browsers can display. XML document XSLT style sheet HTML document XSLT processor

XML - XSLT © 2012 t he University of Greenwich 10 XSLT Processing Does the XSLT processing have to happen at the client side like CSS? No. It often makes sense to do the transformation at the server end and just deliver straight HTML across the web to a variety of browsers Sablotron from Ginger Alliance is an XSLT processor available with Perl and PHP language bindings Xalan from Apache is a Java XSLT processor

XML - XSLT © 2012 t he University of Greenwich 11 XSLT Browsers Internet Explorer –MSXML.dll shipped with IE 5 and 5.5 is non-standard –IE6 uses MSXML3.dll is claimed to be 100% W3C compatible –You can upgrade to MSXML3.dll by installing it Netscape –6 supports some XSLT –7 supports the official W3C XSLT recommendation Mozilla –Uses the open source TransforMiiX module Opera 6+ –supports some XML but not XSLT –policy decision, see ‘Formatting Objects Considered Harmful’ The examples here are tested with IE6, Netscape 6+ and Mozilla (Firefox)

XML - XSLT Stephen Spainhour Webmaster in a Nutshell 1999 O'Reilly COMP1037 Gill Windall Benoît Marchal Applied XML Solutions 2000 Sams COMP goodBookseg1.xml link to XSLT style sheet default rating “ok” character reference

XML - XSLT © 2012 t he University of Greenwich 13 eg1.xsl <xsl:stylesheet version="1.0" xmlns:xsl=" From eg1.xsl xsl: namespace

XML - XSLT goodBooks.eg1.xml

XML - XSLT © 2012 t he University of Greenwich 15 eg1.xsl XML style sheets are written in XML Start with an XML declaration Must include a namespace declaration <xsl:stylesheet version="1.0" xmlns:xsl=" XSLT elements have the form… element content Attributes in normal XML format end tag empty elements are also possible, e.g. name of the XSL element – in this case template xsl: namespace

XML - XSLT © 2012 t he University of Greenwich 16 XSLT language constructs XSLT is a substantially declarative language –as opposed to procedural In declarative languages you specify what you want –as opposed to how you want to achieve it XSLT has more in common with languages such as SQL and Prolog than it does with procedural programming languages such as C or Java –although XSLT does support conditional and iterative constructs XSLT consists of a series of rules that match with things in the source document –specifies what should be output when the match occurs

XML - XSLT © 2012 t he University of Greenwich 17 XSLT templates The view of the input document is a hierarchical tree consisting of nodes XSLT rules are specified as templates to be applied to nodes root node book recommended_books

XML - XSLT © 2012 t he University of Greenwich 18 xsl:template XSLT stylesheets consist of one of more templates. The XSLT processor will attempt to match the templates against the elements in the XML document using a pattern specified by the match= attribute. If the template matches the action (content of the template) will take effect. From eg1.xsl action of the template is inserted into the output document pattern to match – in this case the root element

XML - XSLT © 2012 t he University of Greenwich 19 xsl:value-of An instruction to insert the value of something from the source document into the output document What gets inserted is determined by the select attribute “.” means the current node of the input document –in this case the whole document With client side processing you never see this HTML –if you select "view source" you'll see the original XML document –this can make debugging somewhat difficult From eg1.xsl Stephen Spainhour Webmaster in a Nutshell 1999 O'Reilly COMP1037 Gill Windall Benoît Marchal Applied XML Solutions 2000 Sams COMP1037 Kevin McManus Subrahmanyam Allamaraju Java Server Programming 2000 Wrox COMP1086 Liz Bacon Jennifer Neiderst Web Design in a Nutshell 1999 O'Reilly COMP1037 Gill Windall Daniel Berg Advanced Techniques for Java Developers 1999 Wiley COMP1030 Liz Bacon

XML - XSLT © 2012 t he University of Greenwich 20 eg2.xsl - xsl:apply-templates From eg2.xsl template matching author elements apply a template matching author

XML - XSLT © 2012 t he University of Greenwich 21 author elements from goodBookseg2.xml Note how you get both author/firstname and author/surname

XML - XSLT © 2012 t he University of Greenwich 22 xsl:apply-templates xsl:apply-templates is an instruction that tells the XSLT processor to look for templates that match the pattern specified by the select attribute In eg2.xsl the pattern is //author –any elements called author that exist at any level below the root element in the source XML document The pattern is an XPath expression XPath A pattern matching language used to address specific parts of an XML document. Used within XSLT and other XML technologies such as XLink and XPointer

XML - XSLT © 2012 t he University of Greenwich 23 xsl:apply-templates select="//author" returns a set of nodes corresponding to all of the author nodes in the document xsl:apply-templates then looks for templates to apply to each of them in turn this template will match in turn with each of the author element selected by the previous xsl:apply-templates Match author elements action part of the template specifying what to output

XML - XSLT © 2012 t he University of Greenwich 24 XPath Patterns are used by… –the select= attribute of the xsl:apply-templates instruction –the match= attribute of the xsl:template element Xpath nodes correspond to elements, attributes and text in the XML document XPath patterns are structured similarly to the paths to files and directories book/author/firstname –would match with the “firstname” elements within “author” within “book” When processed Xpath expressions return a data object of one of the following types: –Node set, String, Boolean, Number

XML - XSLT © 2012 t he University of Greenwich 25 XPath abbreviated operators all elements anywhere below root//*wildcard * rating attributes of the all name elements anywhere below the current element.//namecurrent node. all author elements anywhere below the root //author all elements anywhere below the root //recursive descent // / at the start means the root node so this would match book elements directly below the root node /book author elements that are directly contained within book elements book/authorchild / Meaning of exampleExamplesMeaning

XML - XSLT © 2012 t he University of Greenwich 26 Quick Quiz From Quiz a) From Quiz b) what will appear in a browser when these style sheets are applied to goodBooks.xml?

XML - XSLT © 2012 t he University of Greenwich 27 Quick Quiz From Quiz c) From Quiz d) …and with these style sheets?

XML - XSLT © 2012 t he University of Greenwich 28 Quick Quiz From Quiz e) - rated as : - …and finally

XML - XSLT © 2012 t he University of Greenwich 29 eg3.xsl

XML - XSLT <xsl:stylesheet version="1.0" xmlns:xsl=" From eg3.xsl - books in title order title author eg3.xsl for each book sort by title output title then author match anything output as a table column start an HTML table end of the table

XML - XSLT © 2012 t he University of Greenwich 31 eg3.xsl It's possible to do things with XSLT that aren't remotely possible with CSS! This example reorders the list of books and for each book changes the order of elements (author comes before title in the XML document) xsl:for-each is a loop construct much as you would expect in other procedural programming languages xsl:sort allows you to sort elements Can also specify descending order pattern to match

XML - XSLT © 2012 t he University of Greenwich 32 Quick Quiz What order would you expect the books to appear in if the code were changed to:

XML - XSLT From eg4.xsl List in title order / List in course order course title Full book details rating: : eg4.xsl output the rating attribute output the name of the element This is much like the previous example

XML - XSLT Spot the difference? eg4.xsl

XML - XSLT © 2012 t he University of Greenwich 35 eg4.xsl Elements in the XML document are repeated with different formatting in the output document Reading element attribute values using xsl:value-of Using local_name() to return the element name from xsl:value-of : Is that all? No - there are many more features included in XSLT. The next example demonstrates some –A detailed explanation is omitted for brevity but you should have little difficulty figuring out how it works.

XML - XSLT eg5.xsl book rating attribute value converted to a * rating anchor tags link to the full book details book titles in bold

XML - XSLT © 2012 t he University of Greenwich 37 From eg5.xsl List in title order / eg5.xsl

XML - XSLT List in course order course title stars WAT assign the value of the course element to a variable test the value of the variable eg5.xsl

XML - XSLT Full book details # * ** *** convert the value of the book rating attribute to stars eg5.xsl form an anchor tag linking to a named anchor in the output document call a named template

XML - XSLT rating : : create a named anchor with the name of the book eg5.xsl output the title in bold don’t output the title again unabbreviated XPath relative location path

XML - XSLT © 2012 t he University of Greenwich 41 eg5.xsl The links (anchors) take the reader to internal named targets –e.g. –could just as easily reference external URLs –these could be provided in the XML Two different conditional constructs are used –xsl:if –xsl:choose xsl:when xsl:otherwise forms a case statement Named template full-details operates like a function –xsl:param can be used to pass parameters to named templates xsl:variable is used to store the course code value –xsl:variable is more like a constant in that it can be assigned only once –except in this example! – outputs the value of the variable $courseCode rather like an echo statement Unabbreviated XPath location self::title No template is provided for course! –the default template is Combination of XSLT and CSS technologies

XML - XSLT © 2012 t he University of Greenwich 42 XSLT server side processing XSL processing on the server means that plain HTML (XHTML) is returned to the browser Browser compatibility problems are avoided. A number of server side XSL processing possibilities are available: –Java –Perl –ASP –PHP PHP uses the Sablotron XSLT processor from Ginger Alliance. Sablotron is an open source multi-platform XSLT, DOM and Xpath processor –built on James Clark’s expat XML parser.

XML - XSLT XSLT processing with PHP Requires that PHP is configured to support XSLT

XML - XSLT © 2012 t he University of Greenwich 44 <?php error_reporting(15); $xh = xslt_create(); xslt_set_base($xh, 'file:///home/mk05/public_html/web/XML/XSLT/'); $result=xslt_process($xh, 'goodBooks.xml', 'eg6.xsl'); if ($result) { echo " \n"; echo $result; } else { echo "There is an error in the XSL transformation...\n"; echo "\tError number: ". xslt_errno($xh). "\n"; echo "\tError string: ". xslt_error($xh). "\n"; exit; } xslt_free($xh); ?> eg6.php create an XSLT processor apply the XSLT to the XML output the resulting XHTML Set a path to the XML and XSLT free resources after use

XML - XSLT © 2012 t he University of Greenwich 45 eg6.php

XML - XSLT © 2012 t he University of Greenwich 46 eg6.php See the PHP documentation for details –the current version of Sablotron is Begin by creating an XSLT processor $xh = xslt_create(); Then pass the XSLT processor and XML containers with the source XML and the XSLT to xslt_process() $result=xslt_process($xh, 'goodBooks.xml', 'eg6.xsl'); The results of processing $result is returned to the browser and the processor resources liberated xslt_free(); The XSLT is the same as Example 3

XML - XSLT © 2012 t he University of Greenwich 47 Quick Quiz What are the relative merits of processing XSLT client-side or server-side?

XML - XSLT © 2012 t he University of Greenwich 48 eg7.xsl

XML - XSLT Server side transform from eg7.xsl - data entered intro a form eg7.xsl

XML - XSLT © 2012 t he University of Greenwich 50 eg7.xsl This example creates an XHTML form for each book in the XML –allows the user to choose which book is to be inserted into the MySQL database xsl:attribute passes the value of the XML element into an attribute enclosing HTML element The form action is a simple PHP script insert.php that inserts and displays the POST data from the form This XSLT transformation could take place at either the client or the server

XML - XSLT © 2012 t he University of Greenwich 51 Summary CSS and XSL can be used to add presentation details to XML documents. XSL consists of XSLT (transforms) and XSL-FO (formatting objects) –We've only looked at XSLT here. XSL is more powerful than CSS –it can transform the structure of a document and add CSS styling information XSLT is itself an XML language and uses XML syntax XSLT can transform an XML document into any other text based format –e.g. another XML document. For display by a browser XSLT is often used to transform XML into XHTML Transformation may take place at the browser side or the server side so that XHTML is delivered to the browser. XSLT works by matching elements in the source document and specifying the output to generate when a match occurs –uses XPath pattern matching

XML - XSLT © 2012 t he University of Greenwich 52 Questions?