XSLT

1
XSLT

• Brent P. Christie
• Major USMC

2
XSLT Overview

• What is XSLT?
• 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 in a
  separate brief.
• 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.

3
XSLT Overview

• Example of XML document
• lt?xml version1.0?gt
• lt?xml-stylesheet typetext/xml
  hrefplanets.xsl?gt
• ltPLANETSgt
•  
• ltPLANETgt
• ltNAMEgtMercurylt/NAMEgt
• ltMASS UNITS(Earth 1)gt.0553lt/MASSgt
• ltDAY UNITSdaysgt58.65lt/DAYgt
• ltRADIUS UNITSmilesgt1516lt/RADIUSgt
• ltDENSITY UNITS(Earth
  1)gt.983lt/DENSITYgt
• ltDISTANCE UNITSmillion
  milesgt43.4lt/DISTANCEgtlt!--At perihelion--gt
• lt/PLANETgt
•  

4
XSLT Overview

• XML document example cont
• ltPLANETgt
• ltNAMEgtVenuslt/NAMEgt
• ltMASS UNITS(Earth 1)gt.815lt/MASSgt
• ltDAY UNITSdaysgt116.75lt/DAYgt
• ltRADIUS UNITSmilesgt3716lt/RADIUSgt
• ltDENSITY UNITS(Earth
  1)gt.943lt/DENSITYgt
• ltDISTANCE UNITSmillion
  milesgt66.8lt/DISTANCEgtlt!--At perihelion--gt
• lt/PLANETgt
•  
• ltPLANETgt
• ltNAMEgtEarthlt/NAMEgt
• ltMASS UNITS(Earth 1)gt1lt/MASSgt
• ltDAY UNITSdaysgt1lt/DAYgt
• ltRADIUS UNITSmilesgt2107lt/RADIUSgt
• ltDENSITY UNITS(Earth 1)gt1lt/DENSITYgt
• ltDISTANCE UNITSmillion
  milesgt128.4lt/DISTANCEgtlt!--At perihelion--gt
• lt/PLANETgt
•  

5
XSLT Overview

• Example of a style sheet planet.xsl
• lt?xml version1.0?gt
• ltxslstylesheet version1.0 xmlnsxslhttp//ww
  w.w3.org/1999/XSL/Transformgt
•  
• ltxsltemplate matchPLANETSgt
• ltHTMLgt
• ltxslapply-templates/gt
• lt/HTMLgt
• lt/xsltemplategt
•  
• ltxsltemplate matchPLANETgt
• ltPgt
• ltxslvalue-of selectNAME/gt
• lt/Pgt
• lt/xsltemplategt
•  
• lt/xslstylesheetgt

6
XSLT Overview

• Result
• ltHTMLgt
•  
• ltPgtMercurylt/Pgt
•  
• ltPgtVenuslt/Pgt
•  
• ltPgtEarthlt/Pgt
•  
• lt/HTMLgt

7
XSLT Overview

• 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.
• Note the pattern / matches the root node of
  the document, we will see this later
• 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.
• xslvalue-of extracts data from selected
  sub-nodes.

8
XSLT Overview

• We have an XML document and the style sheet (or
  rules) to transform it. So, how do you transform
  the document?.
• You can transform documents in three ways
• In the server. A server program, such as a Java
  servlet, can use a style sheet to transform a
  document automatically and serve it to the
  client. Example, XML Enabler, which is a servlet
  that youll find at XML for Java Web site,
  www.alphaworks.ibm.com/tech/xml4j
• In the client. 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
  servers document directory.
• In any case, a suitable program takes an XML
  document as input, together with an XSLT
  style-sheet.

9
Format of Style Sheet

• You guessed it, XSLT style sheet is itself an XML
  document.
• We will be using the XSLT elements from the
  namespace http//www.w3.org/1999/XSL/Transform
  for this brief
• As a matter of convention we use the prefix xsl
  for this namespace.
• The document root in an XSLT style sheet is an
  xslstylesheet element, e.g.
• ltxslstylesheet version"1.0"
• xmlnsxsl"http//www.w3.org/1999/XSL/
  Transform" gt
• . . .
• lt/xslstylesheetgt
• A synonym for xslstylesheet is xsltransform.
• Several kinds of element can be nested inside
  xslstylesheet, but by far the most important is
  the xsltemplate element.

10
The xsltemplate element

• When you match or select nodes, a template tells
  the XSLT processor how to transform the node for
  output
• So all our templates will have the form
• ltxsltemplate
  matchpatterngt
• template body
• lt/xsltemplategt
• 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.

11
XPATH

• The XML Path Language, or XPath, is a language
  for addressing parts of an XML document.
• The patterns and other node selections appearing
  in XSLT rules are represented using XPath syntax.
• Including the match element of xsltemplate or
  the select element of xslvalue-of.
• Weve seen that you can use the match attribute
  to find nodes by name, child elements(s),
  attributes. Can even find a descendant.
• XPath does all this and more with the select
  attribute.
• Finding nodes by parent or sibling elements, as
  well as much more involved tests.
• More of a true language than the expressions you
  can use with match attribute
• Return not only lists of nodes, but also Boolean,
  string, and numeric values

12
XPath

• It is an essential part of XSLT, and also
  XPointer (as wel as being used in XML schema).
• 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

13
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 64-bit
  IEEE 754 floating-point double-precision format,
  although they may be written and used as an
  integer.
• A string.
• In the end we are interested in Xpath expressions
  that evaluate to a node-set, although other
  expression types will appear.

14
Xpath Node

• XSL transformations accept a document tree as
  input and produce a tree as output. From the XSLT
  point of view, documents are trees built of
  nodes, and there are seven types of nodes that
  can appear in a node-set here are those nodes,
  and how XSLT processors treat them
• Node Description
• Document root Is the very start of the
  document, /
• Attribute Holds the value of an attribute after
  entity references have been expanded and
  surrounding whitespace has been trimmed
• Comment Holds the text of a comment, not
  including lt!-- and --gt
• Element Consists of all character data in the
  element, which includes character data in any
  of the children of the element
• Namespace Holds the namespaces URI
• Processing instruction Holds the text of the
  processing instruction, which does not
  include lt? and ?gt
• Text Holds the text of the node

15
Location paths

• The most important kind of Xpath expressionthe
  one that gives XPath its nameis the location
  path.
• absolute location path path from the root node
• relative starting with current node, called
  context node.
• In general a location path consists of a series
  of location steps separated by the slash /.
  Made up of
• axis, a node test, and zero or more predicates.
• As noted earlier, the most common example of a
  location stepanalogous to a UNIX directory
  nameis 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

16
Parts of a location step

• An individual location step has three logical
  parts
• The axisa 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 testthis 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 . . .

17
Axes

• Any location step starts from some context node
  the axis is relative to this node.
• The available axes are
• childcontains the children of the context node.
• descendentcontains children and all descendents
  of children.
• parentcontains the parent of the context node.
• ancestorcontains parent of the context node and
  ancestors of parent. All the way back to and
  including root node.
• attributecontains the attributes of the context
  node.
• followingall following element nodes, in
  document order.
• precedingall preceding element nodes, in
  document order.
• following-sibling, preceding-siblingelements at
  the same syntactic level.
• namespacecontains namespace nodes of context
  node.
• self, descendent-or-self, ancestor-or-self

18
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, the processing-instruction() function
  may include a literal string specifying a
  particular type of instruction.

19
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 nodesafter
  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.

20
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

21
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() gt 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.

22
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.

23
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.

24
Booleans

• In general an Xpath expression is converted to a
  booleanif context demandsby 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.

25
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-value of 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.

26
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.

27
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 _at_.
• // is short for /descendent-or-self node()/
• e.g //para is short for any para element in the
  document.

28
An input document

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt?xml-stylesheet type"text/xml" href"eg.xsl"?gt
• ltplanetsgt
• ltplanetgt
• ltnamegtMercurylt/namegt
• ltmassgt0.0553lt/massgt
• ltday units"days"gt58.65lt/daygt
• ltradius units"miles"gt1516lt/radiusgt
• ltdensitygt0.983lt/densitygt
• lt/planetgt
• ltplanetgt
• ltnamegtVenuslt/namegt
• ltmassgt0.815lt/massgt
• ltday units"days"gt116.75lt/daygt
• ltradius units"miles"gt3716lt/radiusgt
• ltdensitygt0.943lt/densitygt
• lt/planetgt
• ltplanetgt
• ltnamegtEarthlt/namegt

Simplified version of example from the Inside
XML book (complete with astronomical errors).
29
Using an empty style sheet

• Consider the example where there are no templates
  explicitly specified, eg.xsl has the form
• lt?xml version"1.0" encoding"UTF-8"?gt
• ltxslstylesheet version"1.0"
• xmlnsxsl"http//www.w3.org/1999/XSL/Trans
  form" gt
• lt/xslstylesheetgt
• The transformation of the input document is
• Mercury0.055358.6515160.983Venus0.815116.7537160.9
  43Earth1121071
• i.e. just the concatenated string values in
  all text nodes.
• This happens because there is a default template
  rule
• ltxsltemplate matchtext()gt
• ltxslvalue-of select./gt
• lt/xsltemplategt

30
Templates without embedded XSLT

• Now consider a single template, with no embedded
  XSLT commands
• lt?xml version"1.0" encoding"UTF-8"?gt
• ltxslstylesheet version"1.0
• xmlnsxsl"http//ww
  w.w3.org/1999/XSL/Transform" gt
• ltxsltemplate match"planet"gt
• ltpgtplanet discoveredlt/pgt
• lt/xsltemplategt
• lt/xslstylesheetgt
• The transformation of the input document is
• lt?xml version"1.0" encoding"UTF-16"?gtltpgtplanet
• discoveredlt/pgtltpgtplanet discoveredlt/pgtltpgtplanet
  discoveredlt/pgt
• This is valid HTML, but not very readable
  (as text).
• We can add the command
• ltxsloutput indent"yes"/gt
• to the xslstylesheet element to get
  prettier output formatting.

31
The xslapply-templates element

• Suppose a second template matching the planets
  element is added
• ltxsltemplate
  match"planet"gt
• ltpgtplanet
  discoveredlt/pgt
• lt/xsltemplategt
• ltxsltemplate
  match"planets"gt
• lth1gtAll Known
  Planetslt/h1gt
• lt/xsltemplategt
• The output now only contains the header
• lth1gtAll Known
  Planetslt/h1gt
• 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
  ltxslapply-templatesgt instruction
• ltxsltemplate
  match"planets"gt
• lth1gtAll Known
  Planetslt/h1gt
• ltxslapply-template
  s/gt
• lt/xsltemplategt

32
The xslvalue-of element

• We can now match arbitrary nodes in the source
  document, but we dont yet have a way to extract
  data from those nodes.
• To do this we need the xslvalue-of element,
  e.g.
• ltxsltemplate match"planet"gt
• ltpgtplanet ltxslvalue-of
  select"name"/gt discoveredlt/pgt
• lt/xsltemplategt
• ltxsltemplate match"planets"gt
• lth1gtAll Known Planetslt/h1gt
• ltxslapply-templates/gt
• lt/xsltemplategt
• We now get the more interesting output
• lth1gtAll Known
  Planetslt/h1gt
• ltpgtplanet Mercury
  discoveredlt/pgt
• ltpgtplanet Venus
  discoveredlt/pgt
• ltpgtplanet Earth
  discoveredlt/pgt

33
Selections

• The select attribute of the xslvalue-of element
  is a general Xpath expression.
• Its resultwhich may be a node set or other
  allowed valueis 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.

34
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
• ltplanet name "ltxslvalue-of
  select'name'/gt" gt
• Status discovered
• lt/planetgt
• 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
• ltplanet name "name" gt
• Status discovered
• lt/planetgt
• The Xpath expression name is evaluated exactly as
  for a select attribute, and interpolated into the
  attribute value string.

35
The xslelement element

• For similar reasons we cannot use ltxslvalue-ofgt
  to compute an expression that is used as the name
  of an element in the generated file.
• Instead one can use instead the xslelement
  element.
• These can optionally include nested xslattribute
  elements (as their first children)
• ltxsltemplate match"planet"gt
• ltxslelement name"name"gt
• ltxslattribute name"distance"gt
• ltxslvalue-of select"distance"/gt
  
• lt/xslattributegt
• Status discovered
• lt/xslelementgt
• lt/xsltemplategt
• When this template matches a planet, it generates
  an XML element whose name is the planet, with a
  distance attribute.

36
A Table of Planets

• ltxsltemplate match"planets"gt
• lthtmlgtltbodygt
• lth1gtAll Known Planetslt/h1gt
• lttable width"100" align"center"
  border"1"gt
• lttrgtltthgtnamelt/thgtltthgtmasslt/thgtltthgtdens
  itylt/thgt
• ltthgtradiuslt/thgtlt/trgt
• ltxslapply-templates/gt lt!-- rows of
  table --gt
• lttrgt
• lttdgtAVERAGESlt/tdgt
• lttdgt
• ltxslvalue-of
• select"sum(planet/density
  ) div count(planet)"/gt
• lt/tdgt
• lttdgtlt/tdgt
• lttdgtlt/tdgt
• lt/trgt
• lt/tablegt
• lt/bodygtlt/htmlgt
• lt/xsltemplategt

37
A row of the table

• ltxsltemplate match"planet"gt
• lttrgt
• lttdgtltxslvalue-of select"name"/gtlt/tdgt
  
• lttdgtltxslvalue-of select"mass"/gtlt/tdgt
  
• lttdgtltxslvalue-of select"density"/gtlt/
  tdgt
• lttdgtltxslvalue-of select"radius"/gtlt/t
  dgt
• lt/trgt
• lt/xsltemplategt

38
The display
39
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
• Nancy McCracken, Ozgur Balsoy
• http//aspen.csit.fsu.edu/webtech/xml/

40
XML and Related Acronyms

• Document Type Definition (DTD), which defines the
  tags and their relationships
• Extensible Style Language (XSL) style sheets,
  which specify the presentation of the document
• Cascading Style Sheets(CSS) less powerful
  presentation technology without tag mapping
  capability
• XPATH which specifies location in document
• XLINK and XPOINTER which defines link-handling
  details
• Resource Description Framework (RDF), document
  metadata
• Document Object Model (DOM), API for converting
  the document to a tree object in your program for
  processing and updating
• Simple API for XML (SAX), serial access
  protocol, fast-to-execute protocol for processing
  document on the fly
• XML Namespaces, for an environment of multiple
  sets of XML tags
• XHTML, a definition of HTML tags for XML
  documents (which are then just HTML documents)
• XML schema, offers a more flexible alternative to
  DTD