Web Data Management

1
Web Data Management

• XPath

2
In this lecture

• Review of the XPath specification
• data model
• examples
• syntax
• Resources
• A formal semantics of patterns in XSLT by Phil
  Wadler.
• XML Path Language (XPath) www.w3.org/TR/xpath

3
XPath

• http//www.w3.org/TR/xpath (11/99)
• Building block for other W3C standards
• XSL Transformations (XSLT)
• XML Link (XLink)
• XML Pointer (XPointer)
• XML Query
• Was originally part of XSL

4
XPath

• An expression language to be used in another host
  language (e.g., XSLT, XQuery).
• Allows the description of paths in an XML tree,
  and the retrieval of nodes that match these
  paths.
• Can also be used for performing some (limited)
  operations on XML data.

5
Example for XPath Queries

• ltbibgtltbookgt ltpublishergt Addison-Wesley
  lt/publishergt ltauthorgt Serge
  Abiteboul lt/authorgt ltauthorgt
  ltfirst-namegt Rick lt/first-namegt
  ltlast-namegt Hull lt/last-namegt
  lt/authorgt ltauthorgt Victor
  Vianu lt/authorgt lttitlegt Foundations
  of Databases lt/titlegt ltyeargt 1995
  lt/yeargtlt/bookgtltbook price55gt
  ltpublishergt Freeman lt/publishergt
  ltauthorgt Jeffrey D. Ullman lt/authorgt
  lttitlegt Principles of Database and Knowledge
  Base Systems lt/titlegt ltyeargt 1998
  lt/yeargtlt/bookgt
• lt/bibgt

6
Data Model for XPath

• XPath expressions operate over XML trees, which
  consist of the following node types
• Document the root node of the XML document
• Element element nodes
• Attribute attribute nodes, represented as
  children of an Element node
• Text text nodes, i.e., leaves of the XML tree.

7
Data Model for XPath
The root
Processing instruction
Comment
The root element
book
book
Attr 1
element
attribute
publisher
author
. . . .
Much like the Xquery data model
Addison-Wesley
Serge Abiteboul
text
8
Data Model for XPath

• The root node of an XML tree is the (unique)
  Document node
• The root element is the (unique) Element child of
  the root node
• A node has a name, or a value, or both
• an Element node has a name, but no value
• a Text node has a value (a character string), but
  no name
• an Attribute node has both a name and a value.
• Attributes are special! Attributes are not
  considered as first-class nodes in an XML tree.
  They must be addressed specifically, when needed.

9
XPath Simple Expressions

• /bib/book/year
• Result ltyeargt 1995 lt/yeargt
• ltyeargt 1998 lt/yeargt
• /bib/paper/year
• Result empty (there were no papers)

10
XPath Tree Nodes

• Seven nodes types
• root, element, attribute, text, comment,
  processing instruction and namespace
• Namespace and attribute nodes have parent nodes,
  but are not children of those parent nodes.
• The relationship between a parent node and a
  child node is containment
• Attribute nodes and namespace nodes describe
  their parent nodes

11
Xpath Tree Nodes

• lt?xml version "1.0"?gt
• lt!-- Fig. 11.3 simple2.xml --gt
• lt!-- Processing instructions and namespacess --gt
• lthtml xmlns "http//www.w3.org/TR/REC-html40"gt
• ltheadgt lttitlegtProcessing
  Instruction and Namespace Nodes
• lt/titlegt lt/headgt
• lt?deitelprocessor example
  "fig11_03.xml"?gt
• ltbodygt
• ltdeitelbook deiteledition "1"
  xmlnsdeitel "http//www.deitel.com/
  xmlhtp1"gt ltdeiteltitlegtXML How to
  Programlt/deiteltitlegt lt/deitelbookgt
• lt/bodygt
• lt/htmlgt

12
XPath Tree Nodes

• String-value Each XPath tree node has a string
  representation that XPath uses to compare nodes.
• The string-value of a text node consists of the
  character data contained in the node.
• Document order Nodes in an XPath tree have an
  ordering that is determined by the order in which
  the nodes appear in the original XML document.
• The reverse document order is the reverse
  ordering of the nodes in a document.
• The string-value for the html element node is
  determined by concatenating the string-values for
  all of its descendant text nodes in document
  order.
• The string-value for element node html is
• Processing Instruction and Namespace NodesXML How
   to Program
• Because all whitespace is removed when the text
  nodes are normalized, there is no space in the
  concatenation.

13
XPath Tree Nodes

• For processing instructions, the string-value
  consists of the remainder of the processing
  instruction after the target, including
  whitespace, but excluding the ending ?gt
• The string-value for the processing instruction
  is
• example  "fig11_03.xml"
• Namespace-node string-values consist of the URI
  for the namespace.
• The string-value for the namespace declaration is
• http//www.deitel.com/xmlhtpl

14
XPath Tree Nodes

• For the root node of the document, the
  string-value is also determined by concatenating
  the string-values of its text-node descendents in
  document order.
• The string-value of the root node is therefore
  identical to the string-value calculated for the
  html element node
• The string-value for the edition attribute node
  consists of its value, which is 3.
• The string-value for a comment node consists only
  of the comment's text, excluding lt!-- and --gt.
• The string-value for the second comment node is
  therefore Processing instructions and
  namespacess.

15
XPath Tree Nodes

• Expanded-name Certain nodes (i.e., element,
  attribute, processing instruction and namespace)
  also have an expanded-name that can be used to
  locate specific nodes in the XPath tree.
• Expanded-names consist of both a local part and a
  namespace URI.
• The local part for the element node html is
  therefore html.
• If there is a prefix for the element node, the
  namespace URI of the expanded-name is the URI to
  which the prefix is bound.
• If there is no prefix for the element node, the
  namespace URI of the expanded name is the URI for
  the default namespace.

16
XPath Tree Nodes

• The local part of the expanded name for a
  processing instruction node corresponds to the
  target of the processing instruction in the XML
  document.
• For processing instructions, the namespace URI of
  the expanded-name is null
• The local part of the expanded-name for a
  namespace node corresponds to the prefix for the
  namespace, if one exists or, if it is a default
  namespace, the local part is empty (i.e., the
  empty string).
• The namespace URI of the expanded-name for a
  namespace node is always null.

17
XPath Tree Nodes
Node Type string-value expanded-name Description
root Determined by concatenating the string-values of all text-node descendents in document order. None Represents the root of an XML document. This node exists only at the top of the tree and may contain element, comment or processor-instruction children.
element Determined by concatenating the string-values of all text-node descendents in document order. The element tag, including the namespace prefix (if applicable). Represents an XML element and may contain element, text, comment or processor-instruction children.
attribute The normalized value of the attribute. The name of the attribute, including the namespace prefix (if applicable). Represents an attribute of an element.
text The character data contained in the text node. None. Represents the character data content of an element
comment The content of the comment (not including lt!-- and --gt). None. Represents an XML comment
processing instruction The part of the processing instruction that follows the target and any whitespace The target of the processing instruction. Represents an XML processing instruction
namespace The URI of the namespace The namespace prefix. Represents an XML namespace
18
XPath Axes

• A location path is an expression that specifies
  how to navigate an XPath tree from one node to
  another.
• A location path is composed of location steps,
  each of which is composed of an "axis," a "node
  test" and an optional "predicate."
• Searching through an XML document begins at a
  context node in the XPath tree.
• Searches through the XPath tree are made relative
  to this context node.
• An axis indicates which nodes, relative to the
  context node, should be included in the search.
• The axis also dictates the ordering of the nodes
  in the set.
• Axes that select nodes that follow the context
  node in document order are called forward axes.
• Axes that select nodes that precede the context
  node in document order are called reverse axes.

19
XPath Context

• A step is evaluated in a specific context lt
  N1,N2, ,Nn gt, Nc which consists of
• a context list lt N1,N2, ,Nn gt of nodes from
  the XML tree
• a context node Nc belonging to the context list.
• The context length n is a positive integer
  indicating the size of a contextual list of
  nodes it can be known by using the function
  last()
• The context node position c ? 1,n is a positive
  integer indicating the position of the context
  node in the context list of nodes it can be
  known by using the function position().

20
XPath Steps

• The basic component of XPath expression are
  steps, of the form axisnode-testP1P2. .
  . Pn
• axis is an axis name indicating what the
  direction of the step in the XML tree is (child
  is the default).
• node-test is a node test, indicating the kind of
  nodes to select.
• Pi is a predicate, that is, any XPath expression,
  evaluated as a boolean, indicating an additional
  condition. There may be no predicates at all.
• A step is evaluated with respect to a context,
  and returns a node list.

21
Path Expressions

• A path expression is of the form
  /step1/step2/. . . /stepn
• A path that begins with / is an absolute path
  expression
• A path that does not begin with / is a relative
  path expression.
• Examples
• /A/B is an absolute path expression denoting the
  Element nodes with name B, children of the root
  named A
• ./B/descendanttext() is a relative path
  expression which denotes all the Text nodes
  descendant of an Element B, itself child of the
  context node
• /A/B/_at_att1.gt 2 denotes all the Attribute nodes
  _at_att1 whose value is greater than 2.

22
Evaluation of Path Expressions

• Each stepi is interpreted with respect to a
  context its result is a node list.
• A step stepi is evaluated with respect to the
  context of stepi-1. More precisely
• For i 1 (first step) if the path is absolute,
  the context is a singleton, the root of the XML
  tree else (relative paths) the context is
  defined by the environment
• For i gt 1 if N lt N1,N2, ,Nn gt is the
  result of step stepi-1, stepi is successively
  evaluated with respect to the context N,Nj ,
  for each j ? 1,n.
• The result of the path expression is the node set
  obtained after evaluating the last step.

23
Evaluation of Path Expressions

• Evaluation of /A/B/_at_att1
• The path expression is absolute the context
  consists of the root node of the tree.
• The first step, A, is evaluated with respect to
  this context.

24
Evaluation of /A/B/_at_att1

• The result is A, the root element.
• A is the context for the evaluation of the second
  step, B.

25
Evaluation of /A/B/_at_att1

• The result is a node list with two nodes B1,
  B2.
• _at_att1 is first evaluated with the context node
  B1.

26
Evaluation of /A/B/_at_att1

• The result is the attribute node of B1.

27
Evaluation of /A/B/_at_att1

• _at_att1 is also evaluated with the context node
  B2.

28
Evaluation of /A/B/_at_att1

• The result is the attribute node of B2.

29
Evaluation of /A/B/_at_att1

• Final result the node set union of all the
  results of the last step, _at_att1.

30
XPath Axes
Axes Ordering Description
Self None The context node itself.
Parent Reverse The context node's parent, if one exists.
Child Forward The context node's children, if they exist.
Ancestor Reverse The context node's ancestors, if they exist.
ancestor-or-self Reverse The context node's ancestors and also itself.
Descendant Forward The context node's descendants.
descendant-or-self Forward The context node's descendants and also itself.
Following Forward The nodes in the XML document following the context node, not including descendants.
following-sibling Forward The sibling nodes following the context node.
Preceding Reverse The nodes in the XML document preceding the context node, not including ancestors.
preceding-sibling Reverse The sibling nodes preceding the context node.
Attribute Forward The attribute nodes of the context node.
Namespace Forward The namespace nodes of the context node.
31
XPath Axes

• An axis has a principal node type that
  corresponds to the type of node the axis may
  select.
• For attribute axes, the principal node type is
  attribute.
• For namespace axes, the principal node type is
  namespace.
• All other axes have a element principal node
  type.

32
XPath Axes

• Child axis denotes the Element or Text children
  of the context node.
• Important An Attribute node has a parent (the
  element on which it is located), but an attribute
  node is not one of the children of its parent.
• Example childD

33
XPath Axes

• Parent axis denotes the parent of the context
  node.
• The node test is either an element name, or
  which matches all names, node() which matches all
  node types.
• Always a Element or Document node, or an empty
  node-set (if the parent does not match the node
  test or does not satisfy a predicate).
• .. is an abbreviation for parentnode() the
  parent of the context
• Example parentnode()

34
XPath Axes

• Attribute axis denotes the attributes of the
  context node.
• The node test is either the attribute name, or
  which matches all the names.
• Example attribute

35
XPath Axes

• Descendant axis all the descendant nodes, except
  the Attribute nodes.
• The node test is either the node name (for
  Element nodes), or (any Element node) or text()
  (any Text node) or node() (all nodes).
• The context node does not belong to the result
  use descendant-or-self instead.
• Example descendantnode()

36
XPath Axes

• Example descendant

37
XPath Axes

• Ancestor axis all the ancestor nodes.
• The node test is either the node name (for
  Element nodes), or node() (any Element node, and
  the Document root node).
• The context node does not belong to the result
  use ancestor-or-self instead.
• Example ancestornode()

38
XPath Axes

• Following axis all the nodes that follows the
  context node in the document order.
• Attribute nodes are not selected.
• The node test is either the node name, text()
  or node().
• The axis preceding denotes all the nodes that
  precede the context node.
• Example followingnode()

39
XPath Axes

• Following sibling axis all the nodes that
  follows the context node, and share the same
  parent node.
• Same node tests as descendant or following.
• The axis preceding-sibling denotes all the nodes
  the precede the context node.
• Example following-siblingnode()

40
Location Path Abbreviations
Location path Abbreviation
child This location path is used by default if no axis is supplied and may therefore be omitted
attribute _at_
/descendant-or-selfnode()/ //
selfnode() (.)
parentnode() (..)
41
XPath Node Tests

• The set of selected nodes is refined with node
  tests.
• node tests rely upon the principal node type of
  an axis for selecting nodes in a location path

Node Test Description
Selects all nodes of the same principal node type.
node() Selects all nodes, regardless of their type.
text() Selects all text nodes.
comment() Selects all comment nodes.
processing-instruction() Selects all processing-instruction nodes.
node name Selects all nodes with the specified node name.
42
XPath Axes

• Location Paths Using Axes and Node Tests
• Location paths are composed of sequences of
  location steps.
• A location step contains an axis and a node test
  separated by a double-colon () and, optionally,
  a "predicate" enclosed in square brackets ( ).
• child
• The above location path selects all element-node
  children of the context node, because the
  principal node type for the child axis is
  element.

43
XPath Wildcard

• //author/child or //author/
• Result ltfirst-namegt Rick lt/first-namegt
• ltlast-namegt Hull lt/last-namegt
• Matches any element

44
XPath Axes and Node Tests

• childtext()
• selects all text-node children of the context
  node
• Combining two location steps to form the location
  path
• child/childtext()
• selects all text-node grandchildren of the
  context node

45
XPath Node Tests

• /bib/book/author/text()
• Result Serge Abiteboul
• Victor Vianu
• Jeffrey D. Ullman
• Rick Hull doesnt appear because he has
  firstname, lastname
• /bib/book/author//text()
• Result Rick
• Hull

46
XPath Restricted Kleene Closure

• select all author element nodes in an entire
  document
• /descendent-or-selfnode()/childauthor
• Instead use the abbreviation
• //author
• Resultltauthorgt Serge Abiteboul lt/authorgt
• ltauthorgt ltfirst-namegt Rick
  lt/first-namegt
• ltlast-namegt Hull
  lt/last-namegt
• lt/authorgt
• ltauthorgt Victor Vianu lt/authorgt
• ltauthorgt Jeffrey D. Ullman
  lt/authorgt
• /bib//first-name
• Result ltfirst-namegt Rick lt/first-namegt

47
XPath Attribute Nodes

• /bib/book/_at_price
• Result 55
• _at_price means that price has to be an attribute

48
XPath Predicates

• Boolean expression, built with tests and the
  Boolean connectors and/or (negation is expressed
  with the not() function)
• a test is
• either an XPath expression, whose result is
  converted to a Boolean
• a comparison or a call to a Boolean function.
• Important predicate evaluation requires several
  rules for converting nodes and node sets to the
  appropriate type.

49
Predicate Evaluation

• A step is of the form axisnode-testP
• First axisnode-test is evaluated one obtains
  an intermediate result I
• Second, for each node in I, P is evaluated the
  step result consists of those nodes in I for
  which P is true.
• /A/B/descendanttext()1

50
Predicate Evaluation

• Beware an XPath step is always evaluated with
  respect to the context of the previous step.
• Here the result consists of those Text nodes,
  first descendant (in the document order) of a
  node B.
• /A/B//text()1

51
XPath Predicates

• lt?xml version "1.0"?gt
• lt!-- Fig. 11.9 books.xml --gt
• lt!-- XML book list --gt
• ltbooksgt
• ltbookgt
• lttitlegtJava How to Programlt/titlegt
• lttranslation edition"1"gtSpanishlt/trans
  lationgt lttranslation edition"1"gtChineselt/trans
  lationgt lttranslation edition"1"gtJapaneselt/tran
  slationgt lttranslation edition"2"gtFrenchlt/trans
  lationgt lttranslation edition"2"gtJapaneselt/tran
  slationgt
• lt/bookgt
• ltbookgt lttitlegtC How to
  Programlt/titlegt lttranslation
  edition"1"gtKoreanlt/translationgt lttranslation
  edition"2"gtFrenchlt/translationgt lttranslation
  edition"2"gtSpanishlt/translationgt lttranslation
  edition"3"gtItalianlt/translationgt lttranslation
  edition"3"gtJapaneselt/translationgt
• lt/bookgt
• lt/booksgt

52
XPath Predicates

• Select the title element node for each book that
  has a Japanese translation
• /books/book/translation.  'Japanese'/../title
• A predicate is a Boolean expression used as part
  of a location path to filter nodes from the
  search.
• Select the edition attribute node for books with
  Japanese translations
• /books/book/translation.  'Japanese'/_at_edition

53
XPath 1.0 Type System

• Four primitive types
• The boolean(), number(), string() functions
  convert types into each other (no conversion to
  nodesets is defined), but this conversion is done
  in an implicit way most of the time.
• Rules for converting to a Boolean
• A number is true if it is neither 0 nor NaN.
• A string is true if its length is not 0.
• A nodeset is true if it is not empty.

Type Description Literals Examples
Boolean Boolean values None true(), not(a3)
Number Floating-point 12, 12.5 1 div 33
String Ch. Strings "to", ti concat(Hello,!)
Nodeset Node set None /a/bc1 or _at_e/d
54
XPath 1.0 Type System

• Rules for converting a nodeset to a string
• The string value of a nodeset is the string value
  of its first item in document order.
• The string value of an element or document node
  is the concatenation of the character data in all
  text nodes below.
• The string value of a text node is its character
  data.
• The string value of an attribute node is the
  attribute value.
• Examples (Whitespace-only text nodes removed)

lta toto"3"gt ltb tititutugtltc /gtlt/bgt
ltdgttatalt/dgt lt/agt
string(/) "tata" string(/a/_at_toto
) "3" boolean(/a/b)
true() boolean(/a/e) false()
55
Operators

• Node-set operators allow to manipulate the node
  sets to form other node sets.

Node-set Operators Description
pipe () union of node-sets (Example node()_at_)
slash (/) Separates location steps
double-slash (//) Abbreviation for the location path /descendant-or-selfnode()/
, -, , div, mod standard arithmetic operators
or, and Boolean operators (Example _at_a and c3)
lt, lt, gt, gt relational operators (Example (alt2) and (agt0))
56
Node-set Functions

• node-set functions perform an action on a
  node-set returned by a location path

Node-set Functions Description
last() returns a number equal to the context size from the expression evaluation context
position() Returns the position number of the current node in the node-set being tested.
count( node-set ) Returns the number of nodes in node-set.
id( string ) Returns the element node whose ID attribute matches the value specified by argument string.
local-name( node-set ) Returns the local part of the expanded-name for the first node in node-set.
namespace-uri( node-set ) Returns the namespace URI of the expanded-name for the first node in node-set.
name( node-set ) Returns the qualified name for the first node in node-set.
57
Node-set Functions

• //book/authorlast()
• Returns the last author child of book node -
  Jeffrey D. Ullman
• //book/authorposition() 3 or
  //book/author3
• Selects the third author element of the book node
• /bookcount()
• return the total number of element-node children
  of the book node
• //book
• selects all book element nodes in the document

58
String Functions
String Function Description
concat(s1,...,sn) concatenates the strings s1, . . . , sn
starts-with(a,b) returns true() if the string a starts with b
contains(a,b) returns true() if the string a contains b
substring-before(a,b) returns the substring of a before the first occurrence of b
substring-after(a,b) returns the substring of a after the first occurrence of b
substring(a,n,l) returns the substring of a of length l starting at index n (indexes start from 1). l may be omitted
string-length(a) returns the length of the string a
normalize-space(a) removes all leading and trailing whitespace from a, and collapse all whitespace to a single character
translate(a,b,c) returns the string a, where all occurrences of a character from b has been replaced by the character at the same place in c
59
Boolean and Number Functions
Functions Decsription
not(b) returns the logical negation of the boolean b
sum(s) returns the sum of the values of the nodes in the nodeset s
floor(n) rounds the number n to the next lowest integer
ceiling(n) rounds the number n to the next greatest integer
round(n) rounds the number n to the closest integer
count(//) returns the number of elements in the
document normalize-space( titi toto ) returns
the string titi toto translate(baba,abcdef,A
BCDEF) returns the string BABA round(3.457)
returns the number 3
60
XPath String functions

• lt?xml version "1.0"?gt
• lt!-- Fig. 11.14 stocks.xsl --gt
• lt!-- string function usage --gt
• ltxslstylesheet version "1.0
• xmlnsxsl "http//www.w3.org/1999/XSL/Tra
  nsform
• ltxsltemplate match "/stocks"gt
  lthtmlgt ltbodygt ltulgt
  ltxslfor-each select "stock"gt
  ltxslif test
  "starts-with(_at_symbol,
  'C')"gt ltligt
  ltxslvalue-of
  select
  "concat(_at_symbol,' - ',name)"/gt
  lt/ligt
  lt/xslifgt lt/xslfor-eachgt
  lt/ulgt lt/bodygt
  lt/htmlgt lt/xsltemplategt
• lt/xslstylesheetgt

• lt?xml version "1.0"?gt
• lt!-- Fig. 11.13 stocks.xml --gt
• lt!-- Stock list --gt
• ltstocksgt
• ltstock symbol "INTC"gt
  ltnamegtIntel Corporationlt/namegt lt/stockgt ltstock
  symbol "CSCO"gt ltnamegtCisco Systems,
  Inc.lt/namegt lt/stockgt ltstock symbol "DELL"gt
  ltnamegtDell Computer Corporationlt/namegt
  lt/stockgt ltstock symbol "MSFT"gt
  ltnamegtMicrosoft Corporationlt/namegt lt/stockgt
  ltstock symbol "SUNW"gt ltnamegtSun
  Microsystems, Inc.lt/namegt lt/stockgt ltstock
  symbol "CMGI"gt ltnamegtCMGI,
  Inc.lt/namegt lt/stockgt
• lt/stocksgt

61
XPath Qualifiers

• /bib/book/authorfirst-name
• Result ltfirst-namegt Rick lt/first-namegt
• /bib/book_at_price lt 60
• /bib/book/author_at_age lt 25
• /bib/book/authortext()

62
XPath Examples

• childA/descendantB B elements, descendant
  of an A element, itself child of the context
  node Can be abbreviated to A//B.
• child/childB all the B grand-children of
  the context node
• descendant-or-selfB elements B descendants of
  the context node, plus the context node itself if
  its name is B.
• childBposition()last() the last child
  named B of the context node. Abbreviated to
  Blast().
• following-siblingB1 the first sibling of
  type B (in the document order) of the context node

63
XPath Examples

• /descendantB10 the tenth element of type B in
  the document.
• Not the tenth element of the document, if its
  type is B!
• childBchildC child elements B that have a
  child element C. Abbreviated to BC.
• /descendantB_at_att1 or _at_att2 elements B that
  have an attribute att1 or an attribute att2
  Abbreviated to //B_at_att1 or _at_att2
• selfB or selfC children elements named B
  or C

64
XPath Summary

• bib matches a bib element
• matches any element
• / matches the root element
• /bib matches a bib element under root
• bib/paper matches a paper in bib
• bib//paper matches a paper in bib, at any depth
• //paper matches a paper at any depth
• paperbook matches a paper or a book
• _at_price matches a price attribute
• bib/book/_at_price matches price attribute in book,
  in bib
• bib/book_at_pricelt55/author/lastname matches

65
The Root and the Root

• ltbibgt ltpapergt 1 lt/papergt ltpapergt 2 lt/papergt
  lt/bibgt
• bib is the document element
• The root is above bib
• /bib returns the document element
• / returns the root
• Why ? Because we may have comments before and
  after ltbibgt they become siblings of ltbibgt

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XPath More Details

• Examples
• childauthor/childlastname author/lastname
• childauthor/descendantzip author//zip
• childauthor/parent author/..
• childauthor/attributeage author/_at_age
• What does this mean ?
• paper/publisher/parent/author
• /bib//addressancestorbook
• /bib//author/ancestor//zip

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XPath Even More Details

• name() the name of the current node
• /bib//name()book same as /bib//book
• What does this mean ? /bib//ancestorname()
  !book
• In a different notation bib.book._
• Navigation axis gives us strictly more power !

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XPath 2.0

• An extension of XPath 1.0, backward compatible
  with XPath 1.0. Main differences
• Improved data model tightly associated with XML
  Schema.
• ? a new sequence type, representing ordered set
  of nodes and/or values, with duplicates allowed.
• ? XSD types can be used for node tests.
• More powerful new operators (loops) and better
  control of the output (limited tree restructuring
  capabilities)
• Extensible Many new built-in functions
  possibility to add user-defined functions.
• XPath 2.0 is also a subset of XQuery 1.0.

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Path expressions in XPath 2.0

• New node tests in XPath 2.0
• Nested paths expressions
• Any expression that returns a sequence of nodes
  can be used as a step

Node tests Description
item() any node or atomic value
element() any element (eq. to child in XPath 1.0)
element(author) any element named author
element(, xsperson) any element of type xsperson
attribute() any attribute
/book/(author editor)/name
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XPath 1.0 Implementations

• libxml2 Free C library for parsing XML documents,
  supporting XPath.
• java.xml.xpath Java package, included with JDK
  versions starting from 1.5.
• System.Xml.XPath .NET classes for XPath.
• XMLXPath Free Perl module, includes a
  command-line tool.
• DOMXPath PHP class for XPath, included in PHP5.
• PyXML Free Python library for parsing XML
  documents, supporting XPath.