SDPL 2001Notes 5.1: Additional XPath & XSLT1 5.1 XPath & XSLT: Additional features n XPath support for –arithmetical operations –processing ID/IDREF cross-references –manipulation of strings n Generating text –for content –for attribute values n Repetition, sorting and conditional processing n Generating numbers n Computational power of XSLT

SDPL 2001Notes 5.1: Additional XPath & XSLT2 XPath: Arithmetical Operations Operations for double-precision (64 bit) floating-point numbers +, -, *, div, mod (same as % in Java) Operations for double-precision (64 bit) floating-point numbers +, -, *, div, mod (same as % in Java) –functions to map numbers to integers: »floor(-1.1) = -2, floor(1.1)=floor(1.5)=1 »ceiling(-1.1) = -1, ceiling(1.1)=ceiling(1.5)=2 »round(-1.1) = -1, round(1.1)= 1, round(-1.5) = -1, round(1.5) = 2

SDPL 2001Notes 5.1: Additional XPath & XSLT3 Cross-referencing Function id selects elements by their unique ID Function id selects elements by their unique ID –NB: ID attributes need to be declared (in DTD or its internal subset; See an example later) n Examples –id('sect:intro') selects the element with unique ID "sect:intro" –id('sect:intro')/para[5] selects the fifth para child of the above element

SDPL 2001Notes 5.1: Additional XPath & XSLT4 String manipulation Equality and inequality of strings can be tested with operators = and != Equality and inequality of strings can be tested with operators = and != –"foo" = 'foo' ; "foo" != "Foo" Functions for concatenation, and for testing for substrings: Functions for concatenation, and for testing for substrings: –concat("dog", "bert") = "dogbert" –starts-with("dogbert", "dog") = true() –contains("dogbert", "gbe") = true()

SDPL 2001Notes 5.1: Additional XPath & XSLT5 XPath: more string functions –substring-before("dogbert", "bert") = substring-before("dogbert", "b") = "dog" –substring-after("dogbert", "g")= "bert" –substring( string, startpos, length? ): »substring("dogbert", 1, 3) = "dog" »substring("dogbert", 3) = "gbert" –string-length("dogbert")=7 –translate( Str, ReplacedChars, ReplacingChars ): »translate("dogbert", "dgo", "Dli") = "Dilbert"

SDPL 2001Notes 5.1: Additional XPath & XSLT6 Computing generated text The string-value of an expression can be inserted in the result tree by instruction The string-value of an expression can be inserted in the result tree by instruction –if the expression evaluates to a node-set, the value of the first node in document order is used n Consider transforming source elements like Charlie Parker Charlie Parker to the form Charlie ("Bird") Parker

SDPL 2001Notes 5.1: Additional XPath & XSLT7 Computing generated text (2) This can be specified by template rule This can be specified by template rule (" ") (" ") Verbatim text (like the linefeed above) can be inserted using xsl:text Verbatim text (like the linefeed above) can be inserted using xsl:text

SDPL 2001Notes 5.1: Additional XPath & XSLT8 Attribute value templates The string-value of an expression can be inserted in an attribute value by surrounding the expression by braces { and } The string-value of an expression can be inserted in an attribute value by surrounding the expression by braces { and } Consider transforming source element Consider transforming source element<photo> Mary.jpg Mary.jpg into form into form

SDPL 2001Notes 5.1: Additional XPath & XSLT9 Attribute value templates (2) Attribute value templates (2) This can be specified by template rule This can be specified by template rule Expressions {file} and are evaluated in the context of the current node (the photo element) Expressions {file} and are evaluated in the context of the current node (the photo element)

SDPL 2001Notes 5.1: Additional XPath & XSLT10 XSLT: Repetition Nodes can be "pulled" from source for processing using instruction Template Nodes can be "pulled" from source for processing using instruction Template –the template is applied to each of the selected nodes (0, 1 or more), each node in turn as the current node »in document order, unless sorted using xsl:sort instructions (see later)

SDPL 2001Notes 5.1: Additional XPath & XSLT11 Example ( xsl:for-each ) n Consider formatting the below document as HTML: ]> The Joy of XML Getting Started Helen Brown says that processing XML documents is fun. Dave Dobrik agrees. Family affairs Bob Brown is the husband of Helen Brown. Finishing Up As we discussed in, processing XML documents is fun. ]> The Joy of XML Getting Started Helen Brown says that processing XML documents is fun. Dave Dobrik agrees. Family affairs Bob Brown is the husband of Helen Brown. Finishing Up As we discussed in, processing XML documents is fun.

SDPL 2001Notes 5.1: Additional XPath & XSLT12 Example: Table of contents n A table of contents can be formed of section titles: Table of Contents Table of Contents

SDPL 2001Notes 5.1: Additional XPath & XSLT13 Example (cont; Cross references) Cross references (to sections) can also be processed using xsl:for-each: Cross references (to sections) can also be processed using xsl:for-each: Section (...) Section (...) With this rule the source fragment With this rule the source fragment As we discussed in As we discussed in becomes As we discussed in Section (Getting …)

SDPL 2001Notes 5.1: Additional XPath & XSLT14 XSLT Sorting A sorted order for the processing of nodes with xsl:for-each and xls:apply-templates can be specified by A sorted order for the processing of nodes with xsl:for-each and xls:apply-templates can be specified by controlled by attributes of xsl:sort like controlled by attributes of xsl:sort like –select : expression for the sort key –data-type : "text" (default) or "number" – order : "ascending" (default) or "descending" The first xsl:sort specifies the primary sort key, the second one the secondary sort key, and so on. The first xsl:sort specifies the primary sort key, the second one the secondary sort key, and so on.

SDPL 2001Notes 5.1: Additional XPath & XSLT15 Example (cont; Sorted index of names) All names can be collected in a last-name-first-name order using the below template All names can be collected in a last-name-first-name order using the below template Index, Index, n This creates an UL list with items Brown, Bob Brown, Helen Brown, Helen Dobrik, Dave Brown, Bob Brown, Helen Brown, Helen Dobrik, Dave

SDPL 2001Notes 5.1: Additional XPath & XSLT16 What about duplicates? Is it possible to eliminate duplicate values like Brown, Helen Brown, Helen ? Is it possible to eliminate duplicate values like Brown, Helen Brown, Helen ? n Yes (but not that straightforward) n Using conditional instructions –See next

SDPL 2001Notes 5.1: Additional XPath & XSLT17 Conditional processing A template can be instantiated or ignored based on the value of a test Boolean expression, using A template can be instantiated or ignored based on the value of a test Boolean expression, using Template Template Example: a comma-separated list of names: Example: a comma-separated list of names:,,

SDPL 2001Notes 5.1: Additional XPath & XSLT18 Conditional processing (2) n Also a case-like construct: … … … … … </xsl:choose>

SDPL 2001Notes 5.1: Additional XPath & XSLT19 Example (cont; Eliminating duplicate names) No access to other nodes (except current() ) in the list of xsl:for-each (?) No access to other nodes (except current() ) in the list of xsl:for-each (?) –But can refer to other nodes in the source tree –Process just the first one of duplicate name s:,,

SDPL 2001Notes 5.1: Additional XPath & XSLT20 Generating numbers Formatted numbers can be inserted in the result tree by element xsl:number Formatted numbers can be inserted in the result tree by element xsl:number –can be specified by attribute value=" Expr " –otherwise the number generated based on the position of the current node in the source tree Example 1, a numbered list: Example 1, a numbered list:

SDPL 2001Notes 5.1: Additional XPath & XSLT21 Generating numbers (2) n Example 2. Hierarchical numbering (1, 1.1, 1.1.1, 1.1.2, …) for titles of chapters, titles of sections of chapters, and titles of subsections of sections

SDPL 2001Notes 5.1: Additional XPath & XSLT22 Generating numbers (3) Example 3. Sequential numbering of note s within chapter s: Example 3. Sequential numbering of note s within chapter s:

SDPL 2001Notes 5.1: Additional XPath & XSLT23 Computational power of XSLT n Programming-like features, for example, –limited variables (names bound to values): … –named templates which can be explicitly called with parameters: … –named templates which can be explicitly called with parameters: …

SDPL 2001Notes 5.1: Additional XPath & XSLT24 Computational power of XSLT n Conditional instructions, string functions and named templates sufficient to simulate Turing machines n Implications: –XSLT has full algorithmic programming power »Is this intentional? »Inconvenient as a general-purpose programming language! –Impossible to recognise non-terminating transformations automatically »Malicious hacker could cause "denial-of-service" through non- terminating style sheets