]> Introduction to XSLT

July 23rd 2001 January 7th 2001 October 15th 2000 July 12th 2000 June 24th 2000 July 25th 1999 Introduction to XSLT Sebastian Rahtz July 2001
What is the XSL family?

XPATH: a language for expressing paths through XML trees XSLT: a language for expressing transformation of XML XSL FO: an XML vocabulary for describing formatted pages The XSLT language is Expressed in XML; uses namespaces to distinguish output from instructions Purely functional Reads and writes XML trees Designed to generate XSL FO

How is XSLT used? (1)

With a command-line program to transform XML (eg to HTML) Downside: no dynamic content, user sees HTML Upside: no server overhead, understood by all clients In a web server servlet, eg serving up HTML from XML Downside: user sees HTML, server overhead Upside: understood by all clients, allows for dynamic changes

How is XSLT used? (2)

In a web browser, displaying XML on the fly Downside: most clients do not understand it Upside: user sees XML Embedded in specialized program As part of a chain of production processes, performing arbitrary transformations

What do you mean, `transformation'?

Take this Pasta for beginners Pasta Grated cheese Cook the pasta and mix with the cheese ]]> and make this

Pasta for beginners

Ingredients: Pasta Grated cheese

Cook the pasta and mix with the cheese ]]>

How do you express that in XSL?

Ingredients:

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XSL Resources XT, Saxon, Xalan, libxslt, Sablotron, Transformiix; Perl/Python etc Oracle XML, uxsl Internet Explorer 5 (upgrade), Mozilla (nearly) FOP, PassiveTeX, XEP, Unicorn
How an XSLT processor works (1)

An XSLT stylesheet has rules for transforming a source tree into a result tree. The transformation is achieved by associating patterns with templates. A pattern is matched against elements in the source tree. A template is instantiated to create part of the result tree, which is separate from the source tree. In constructing the result tree, elements from the source tree can be filtered and reordered, and arbitrary structure can be added.

How an XSLT processor works (2)

When a template is instantiated, each instruction is executed and replaced by the result tree fragment that it creates. Instructions can select and process descendant source elements. Note that elements are only processed when they have been selected by the execution of an instruction. The result tree is constructed by finding the template rule for the root node and instantiating its template.

How an XSLT processor works (3)

When finding the applicable template rule, more than one template rule may have a pattern that matches a given element. However, only one template rule will be applied. XSLT makes use of the XPath expression language for selecting elements for processing, for conditional processing and for generating text. Extension mechanisms are defined for extending the set of instruction elements used in templates and for extending the set of functions used in XPath expressions.

Complete example: input

JohnKeats 000 2421821 0 This Grave contains all that was Mortal, of a YOUNG ENGLISH POET, ]]>

Complete example: stylesheet

Protestant Cemetery Catalogue

Stone

    • ]]>

    XSLT constructs (1)

    Template match against element ]]>

    Process all children ]]>

    Process selected children]]>

    Process children separately Second: ]]>

    XSLT constructs (2) Loop around a set of children
    • ]]>         Print an attribute]]> Put a calculated value in an output attribute ]]> Put out literal text (including spaces) ! ]]>
    XSLT constructs (3) Template match against attributes ]]> Simple test ]]> Case statement Its a boy! Its a girl! Error in data: sex attribute has ]]>
    XSLT constructs (4) Numbering. The default is to provide the sibling number, but you can also make it document-wide: . . . ]]>
    XSLT constructs (5) Sorting
    ]]>
    XSLT constructs (6) Using built-in functions .... ]]>
    XSLT constructs (7) Using axes .... ]]>
    XPATH axes self attribute (shorthand form: @) child (shorthand form: ) descendant (shorthand form: //) descendant-or-self ancestor ancestor-or-self namespace following preceding following-sibling preceding-sibling parent (shorthand form: ..)
    All children

    ]]>

    No children

    ]]>

    Inscriptions

    ]]>

    Death dates of peope on stones

    ]]>

    Person inside stone

    ]]>

    First person on each stone

    ]]>

    Death dates of last person on first stone

    / / ]]>

    Illustration of axes

    Conclusions XSLT is good at expressing typical documentation transformations XPATH has expressive power sufficient for most eventualities The range and number of implementations makes the standard secure XSLT is already widely used at all levels XSLT currently has problems with big documents