1. XPath Kanda Runapongsa (krunapon@kku.ac.th)krunapon@kku.ac.th Dept. of Computer Engineering Khon Kaen University

2. 168493: XML and Web Services (II/2546) 2 What is XPath? XPath is a language designed to address specific parts of an XML document It was designed to be used by both XSLT and XPointer XSLT: transforms an XML document into any text-based format, such as HTML XPointer: the basis for a fragment identifies only for text/xml & application/xml media types

3. 168493: XML and Web Services (II/2546) 3 XPath Expressions The XPath data model views a document as a tree of nodes An instance of the XPath language is called an expression A path expression is an expression used for selecting a node set by following a path or steps

4. 168493: XML and Web Services (II/2546) 4 XPath Expressions (Cont.) XPath use path expressions to identify nodes in an XML document These path expressions look very much like the expressions you see when you work with a computer file system Documents/courses/168493/xpath.ppt

5. 168493: XML and Web Services (II/2546) 5 Sample Document Hide your heart Bonnie Tyler 9.90 Greatest Hits Dolly Parton 10.90

6. 168493: XML and Web Services (II/2546) 6 Path Expressions Examples /catalog This XPath expression selects the ROOT element catalog /catalog/cd This XPath expression selects all the cd elements of the catalog element /catalog/cd/price This XPath expression selects all the price elements of all the cd elements of the catalog element

7. 168493: XML and Web Services (II/2546) 7 / and // / select the root node of the current document Example: /catalog Select the root element catalog An absolute path to an element // select nodes that are the descendant nodes of context node Example: //cd Select the cd elements in the document

8. 168493: XML and Web Services (II/2546) 8 Selecting Unknown Elements Wildcards (*) can be used to select unknown elements /catalog/cd/* This XPath expression selects all the child elements of all the cd elements of the catalog element

9. 168493: XML and Web Services (II/2546) 9 Selecting Unknown Elements (Cont.) /catalog/*/price This expression selects all the price elements that are grandchild elements of the catalog element /*/*/price This expression selects all price elements which have 2 ancestors How to select all elements?

10. 168493: XML and Web Services (II/2546) 10 Selecting Branches By using square brackets in an XPath expression you can specify an element further /catalog/cd[1] The XPath expression selects the first cd child element of the catalog element

11. 168493: XML and Web Services (II/2546) 11 Selecting Branches (Cont.) /catalog/cd[last()] The expression selects the last cd element of the catalog element /catalog/cd[price] The expression selects all the cd elements of the catalog element that have a price element

12. 168493: XML and Web Services (II/2546) 12 Selecting Branches (Cont.) /catalog/cd[price=10.90] Selects all the cd elements of the catalog element that have a price element with a value of 10.90 /catalog/cd[price=10.90]/price Selects all the price elements of all the cd elements of the catalog element that have a price element with a value of 10.90

13. 168493: XML and Web Services (II/2546) 13 Selecting Several Branches By using the | operator in an XPath expression you can select several paths /catalog/cd/title | /catalog/cd/artist Selects all the title and artist elements of the cd element of the catalog element

14. 168493: XML and Web Services (II/2546) 14 Selecting Attributes In XPath all attributes are specified by the @ prefix //@country Selects all attributes named country //cd[@country] Selects all cd elements which have an attribute named country

15. 168493: XML and Web Services (II/2546) 15 Selecting Attributes (Cont.) //cd[@*] Selects all cd elements which have any attribute //cd[@country=‘UK’] Selects all cd elements which have an attribute named country with a value of ‘UK’

16. 168493: XML and Web Services (II/2546) 16 A Location Path It is the most important kind of expressions in the XPath notation It can be absolute or relative An absolute path starts with a slash (/) and a relative location path does not start with a slash The location path consists of one or more location steps, each separated by a slash

17. 168493: XML and Web Services (II/2546) 17 A Location Path (Cont.) An absolute location path: /step/step/… A relative location path: step/step/… The location steps are evaluated in order one at a time, from left to right Each step is evaluated against the nodes in the current node-set

18. 168493: XML and Web Services (II/2546) 18 A location Path (Cont.) The current node-set that is being selected is called the set of the context nodes Each step of a location path (a location step) has three following parts: An axis – specifies the tree relationship between the nodes selected by the location step and the current node A node test – specifies the node type Zero or more predicates – use expressions to further refine the set of nodes

19. 168493: XML and Web Services (II/2546) 19 A Location Step The syntax for a location step is: axisname::nodetest[predicate] Example: child::cd[price=9.90] An axis defines a node-set relative to the current node A node test is used to identify a node with an axis

20. 168493: XML and Web Services (II/2546) 20 Axis Names ancestor: contains all ancestors (parent, grandparent, etc.) of the current node ancestor-or-self: contains the current node plus all its ancestors (parent, grandparent, etc.) What is the node that this axis always includes?

21. 168493: XML and Web Services (II/2546) 21 Axis Names (Cont.) attribute: contains all attributes of the current node child: contains all children of the current node descendant: contains all descendants (children, grandchildren, etc.) of the current node Does this axis contain attribute nodes?

22. 168493: XML and Web Services (II/2546) 22 Axis Names (Cont.) descendant-or-self: contains the current node plus all its descendants following: contains everything in the document after the closing tag of the current node, except descendants following-sibling: contains all siblings after the current node

23. 168493: XML and Web Services (II/2546) 23 Axis Names (Cont.) namespace: contains all namespace nodes of the current node parent: contains the parent of the current node preceding: contains everything in the document that is before the starting tag of the current node, except ancestors

24. 168493: XML and Web Services (II/2546) 24 Axis Names (Cont.) preceding-sibling: contains all siblings before the current node self: contains the current node For any given context node v, the four major axes specify a partitioning of the document containing v v/descendants U v/ancestors U v/following U v/preceding U {v}

25. 168493: XML and Web Services (II/2546) 25 Examples child:cd Selects all cd elements that are children of the current node attribute::src Selects the src attribute of the current node

26. 168493: XML and Web Services (II/2546) 26 Examples (Cont.) child::cd[position() < 6] Selects the first five cd children of the current node child::cd[attribute::type=“classic”] Selects all cd children of the current node that have a type attribute with value classic

27. 168493: XML and Web Services (II/2546) 27 Unabbreviated vs. Abbreviated The name of the location path is long Location paths can be expressed using abbreviated syntax The most important abbreviation is child:: which can be omitted from a location step Example: cd is short for child::cd

28. 168493: XML and Web Services (II/2546) 28 Abbreviated Syntax @ is short for attributes:: Example: cd[@type=“classic”] is short for child::cd[attribute::type=“classic”]. is short for self::node() Example::./cd is short for self::node()/child::cd

29. 168493: XML and Web Services (II/2546) 29 Abbreviated Syntax (Cont.).. is short for parent::node Example:../cd is short for parent::node()/child::cd // is short for /descendant-or-self::node()/ Example:: //cd is short for /descendant-or-self::node()/child::cd

30. 168493: XML and Web Services (II/2546) 30 Examples cd[@type=“classic”] Selects all cd children of the current node that has a type attribute with value classic cd[@type=“classic”][5] Selects the fifth cd child of the current node that has a type attribute with value classic

31. 168493: XML and Web Services (II/2546) 31 Examples cd[5][@type=“classic”] Selects the fifth cd child of the current node if that child has a type attribute with value classic cd[@type and @country] Selects all the cd children of the current node that have both a type attribute and a country attribute

32. 168493: XML and Web Services (II/2546) 32 Node Set Functions Function count() counts the number of selected elements Function name() returns name of the element Function position() returns the position in the node list of the node that is currently being processed

33. 168493: XML and Web Services (II/2546) 33 String Functions Function contains() returns true if the 1 st argument string contains the 2 nd argument string Example: contains(‘XML’, ‘M’) Result: true Function string-length() returns the number of characters in the string Example: string-length(‘XML’) Result: 3

34. 168493: XML and Web Services (II/2546) 34 String Functions (Cont.) Function substring() returns the substring of the first argument starting at the position specified in the 2 nd argument with length specified in the 3 rd argument Example: substring(‘Students’,4,4) Result: ‘dent’

35. 168493: XML and Web Services (II/2546) 35 String Functions (Cont.) Function starts-with() returns true if the first argument starts with the second argument Example: starts-with(‘XML’, ‘X’) Result: true Function string() converts the value argument to a string Example: string(314) Result: ‘314’

36. 168493: XML and Web Services (II/2546) 36 Number Functions celing() returns the smallest integer that is not less than the number argument Example: ceiling(3.14)  4 sum() returns the total value of a set of numeric values in a node-set Example: sum(/cd/price)