XML and Java XSLT - Lecture slides PDF

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Transforming XML XMLNamespaces, XSLT

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XML Namespaces •  Sometimes it is necessary to mix XML elements –  Different types of content –  Use of markup to convey meta-information

•  Some documents combine markup from different XML languages •  But: –  Elements and attributes from different XML languages may share the same name –  Need to group elements for processing 2

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XML Namespaces •  XML Namespaces is the xml standard for distinguishing xml elements •  Namespaces are represented by attributes •  Elements from the same namespace can be recognised by software as a group •  Unique namespaces are defined by a URI

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URL, URN, URI •  URL: a Uniform Resource Locator •  specifies the mechanism by which a resource is accessed •  e.g. http://www.comp.rgu.ac.uk/home.html

•  URN: a Uniform Resource Name •  a unique sequence of characters naming an internet resource e.g. urn:Turquoise.Inflatable.Walrus •  the name has persistence even if the resource becomes unavailable

•  URI –  uniform resource identifier •  a URL or a URN (see RFC 2396 at www.ietf.org)

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the namespace prefix •  •  •  • 

short string representing the namespace URI distinguishes element and attribute names defined using an xmlns:prefix attribute a prefixed element name is called a qualified name, or QName, or a raw name •  QName syntax prefix:local_part 5

example •  SVG and MathML both contain a set element •  Both SVG and MathML can be embedded in XHTML documents •  prefixes svg and mathml are used to distinguish the set elements distinct from 6

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example 2: xml with multiple namespaces

xhtml namespace associated to root Thhtml element and all descendants (no prefix needed)

namespace everywhere within the root element Ellipse and Rectangle

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Richard P Feynman

physicist playing the bongoes

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a simple XSLT example the transforming stylesheet

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•  xsl prefix identifies xsl QNames as belonging in the XSLT namespace associated to the given URI •  the empty stylesheet •  contains no template rules •  will apply default rules (see later) 24

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a simple XSLT example the output of the transform

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Alan Turing computer scientist mathematician cryptographer Richard

default behaviour strips out the mark up and returns a text document that reproduces the content of the XML (including whitespace like tabs and carriage returns)

P Feynman physicist playing the bongoes

to modify the default behaviour, we add template rules that describe how to transform elements of the source document

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template rules •  a template rule is defined by an element •  the match attribute contains a pattern identifying the input to which the rule is applied •  the content of the element is a template for the output from the matched pattern

template

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example 2

A Person

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example 2 output

A Person

Each person element in the original document has been replaced entirely by the template.

A Person

The whitespace outside each person element has been preserved

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example 3

A Person

elements used in a template must preserve well-formedness of the document

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example 3 output

A Person

The and tags have also been copied over from the template

A Person

The whitespace outside each person element has been preserved

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xsl:value-of •  xsl element which extracts the string value of an element in the source XML –  the string value is the text content after: •  all tags have been removed •  entity and character references have been resolved

•  select attribute specifies the element whose value is taken 32

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example 4





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example 4 output Alan Turing

the full text content of the element after the , , and tags have been stripped out

Richard

The whitespace inside each name element has been preserved along with the rest of the text content



P Feynman

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•  xsl element that can affect the default order of processing –  which elements should be processed next –  process elements in the middle of processing another element –  prevent particular elements from being processed

•  select attribute contains a pattern identifying elements to be processed at that point 35

example 5



,



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example 5 output Turing,

The order of processing has been changed.

Alan

The output for each consists of the full text content of the , followed by a comma and a new line, followed by the full text content of the .

Feynman, Richard

The and elements are never processed because bypasses them 37

XSLT processor •  a software component that •  reads a XML source document and a stylesheet •  applies the transformation rules •  outputs the transformed document

•  standalone •  SAXON •  Apache Xalan (used in NetBeans)

•  built into a browser or application server •  MSXML (built in to IE6) •  Apache Cocoon (built in to Apache server) 38

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You need special software to run XSLT •  But you don’t have to buy them •  Free open-source, shareware, as well as commercial •  New ones all the time •  Look for more at: http://www.xml.com –  Saxon (http://users.iclway.co.uk/mhkay/saxon/ ) –  Xalan XSLT (http://xml.apache.org/xalan/index.html ) –  Unicorn XSLT Processor •  (http://www.unicorn-enterprises.com/ )

–  XSLT C library for Gnome (http://xmlsoft.org/XSLT/ ) 39

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