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1 6/3/2016 8:44 PM 1 of 35

2 6/3/2016 8:44 PM 2 of 35 2) Background Well-formed XML HTML XSLT Processing Model

3 6/3/2016 8:44 PM 3 of 35 3) XPath XPath locates items within an XML file It relies on the XML tree structure to locate elements XPath is used within XSLT elements to identify what to bring from the input XML file to the result tree An XPath looks like a path through an XML tree

4 6/3/2016 8:44 PM 4 of 35 4) Nodes and Node Sets A given XPath may identify one node in the input tree: a node Or it may identify several nodes in the input tree: a node set

5 6/3/2016 8:44 PM 5 of 35 5) Using XPaths XPath is used in almost all XSLT elements. For this topic, we will use two. <xsl:value-of select="xpath"/> value-of takes the XPATH, chooses the first node in the node set if there is more than one, and then puts all of the content nodes within that node into the result tree as one flat content node. A nested element is looked within for content. Attributes within elements are not included. Example: <xsl:value-of select="/members/member/name"/>

6 6/3/2016 8:44 PM 6 of 35 6) Using XPaths (part 2) <xsl:copy-of select="xpath"/> copy-of takes the XPATH, and copies the entire node set to the result tree, including all nested nodes. It includes attributes. If you aren't sure if you have identified multiple nodes, use both value-of and copy-of to see if they both find a single node or not. Example: <xsl:copy-of select="/members/member/name"/>

7 6/3/2016 8:44 PM 7 of 35 7) XPath Absolute path starts at the root node: "/" Relative path starts relative to the current context node. xsl:template and xsl:for-each set the current context node (see later videos)

8 6/3/2016 8:44 PM 8 of 35 8) Choosing an element To reach the element first in members.xml, starting at root: /members/member/name/first Use / to denote the root Name the root element (members) Use a / to go down a level Add the next element under that closer to your element (member) Repeat those two steps until you reach the element you want. (/name/first)

9 6/3/2016 8:44 PM 9 of 35 9) Picking a particular element When there is more than one element at a given level, you will search in that node set if you continue looking within, unless you use an index to specify which one you want. /members/member[2]/name/first This bypasses Bob and goes to Mary. Indexes start at 1 for the first one.

10 6/3/2016 8:44 PM 10 of 35 10) Choosing an attribute To reach the attribute amt in pudding.xml, starting at root: Build a path to reach the element the attribute is on (/recipe/ingredients/li) Use a / to look within that last element Add the attribute with prefix on it (@amt) value-of shows the contents; copy-of expects to place it on an element, and since duplicate attributes are not permitted, picks the last one

11 6/3/2016 8:44 PM 11 of 35 11) XPath shorthands If you have a current context (from a template or a for-each), you don't need to start at root. Shorthands relative to the current node:. : current node.. : parent node : all immediate children // : any depth, used in place of a / in an XPath Example: <xsl:value-of select="//name"/> Matches all names, value-of gets the first one and displays its contents, so Bob Smith is output.

12 6/3/2016 8:44 PM 12 of 35 12) XPath location functions Some nodes do not have names; these can be accessed using XPath functions comment() : locates comment nodes processing-instruction() : locates processing text() : locates content nodes, available on Example: <xsl:copy-of select="//text()"/> outputs all of the content nodes under elements in the tree. note members.xml and pudding.xml have no processing instruction or comments

13 6/3/2016 8:44 PM 13 of 35 13) XPath predicates A predicate is a test that chooses from the current matching nodes. Add a predicate by putting it in square braces on an XPath item, for example: <xsl:value-of select="/members/member[member_ If this matches more than one, you still have a node set, and if needed, XSL will choose the first one. The current context within the predicate is the current XPath up to that point. If there is no test, then it tests for existence: does the specified node exist.

14 6/3/2016 8:44 PM 14 of 35 14) XPath predicate tests You can compare two values: =!= : Equals / Not Equals > >= : Greater / Greater or Equal < <= : Less / Less or Equal if one side is a number, then the other is converted to a number; otherwise string comparison is used You can call a function that returns a boolean value You can combine tests with and (both have to be true) or or (only one has to be true).

15 6/3/2016 8:44 PM 15 of 35 15) XPath predicate test example Look for names with m in the last name (try this in both value-of and copy-of, on members.xml): //name[contains(last,'m')]

16 6/3/2016 8:44 PM 16 of 35 16) XPath functions provide information about the current node set provide information about the current node manipulate strings manipulate numbers manipulate booleans

17 6/3/2016 8:44 PM 17 of 35 17) XPath node set functions last(), count() : the number of nodes in the current node set last(xpath), count(xpath) : the number of nodes in the specified XPath node set sum(xpath) : converts all nodes identifed to numbers and adds them up.

18 6/3/2016 8:44 PM 18 of 35 18) XPath node set function examples Add up all members' balances: <xsl:value-of select= "sum(/members/member/member_data/balance)

19 6/3/2016 8:44 PM 19 of 35 19) XPath node information functions name() : the name of the current node, if it has one node() : the current node, equivalent to "." shorthand. text() : the content of the current node, if it has any, as text position() : the position of the current node within a node set, or 1 if it is not in a node set; position is defined by order within the source XML file.

20 6/3/2016 8:44 PM 20 of 35 20) XPath node information function examples The position of the current node (1 if not in a node set) <xsl:value-of select="position()"/> The text in all the first name nodes <xsl:copy-of select="/members/member/name/fir

21 6/3/2016 8:44 PM 21 of 35 21) XPath string functions concat(string1,string2,...) : combine two or more strings contains(string1,string2) : true if STRING2 is found within the value of STRING1. number() : converts value to a number; string must be digits, booleans are 0/1. starts-with(string1,string2) : true if STRING1 starts with STRING2 string() : converts the current node's value to a string string-length() : the length of the text in the current node

22 6/3/2016 8:44 PM 22 of 35 22) XPath string functions, continued substring(string,start,end) : extracts a portion of the string. substring-after/substringbefore(string,substring) : extracts a portion of STRING text() : the text contents of the current node, if it has any translate() : a simple transformation of a string based on a character map String literals are characters enclosed in single or double quotes, following XML rules for values within quotes and using quotes (like attribute values) Any parameter can be an XPATH returning a node; its contents will be used as the value.

23 6/3/2016 8:44 PM 23 of 35 23) XPath string function examples Name of first member with e in their last name: <xsl:value-of select= "/members/member/name[contains(last,'e')] Try this with copy-of to see all the matches.

24 6/3/2016 8:44 PM 24 of 35 24) XPath number functions +,-,*,div,mod : inline, i.e mod is "modulus", or remainder of division floor(value)/ceiling(value) /round(value) : truncates or rounds value to nearest integer number(value) : converts strings and booleans to numbers sum(xpath) : adds up all the numeric values in the node set Number literals are, for example, 1 or VALUE can be an XPATH that identifies a numeric value or a number literal

25 6/3/2016 8:44 PM 25 of 35 25) XPath number function examples Show the member balance with the annual membership fee deducted <xsl:value-of select= "/members/member/member_data/balance - Note, this doesn't change the xml file, it just displays the modified value.

26 6/3/2016 8:44 PM 26 of 35 26) XPath boolean functions and, or : inline to combine two boolean tests. 'and' is true if both are true, 'or' is true if either is true. boolean(value) : converts values to booleans; 0 and empty strings are false. contains(string1,string2) : true if STRING1 contains STRING2 false() : boolean false value not(value) : reverses a boolean value starts-with(string1,string2) : true if STRING1 starts with STRING2 true() : boolean true value Parameters can be XPaths or literals If not booleans, they are implicitly converted

27 6/3/2016 8:44 PM 27 of 35 27) XPath boolean function examples Find a member with a title and with a positive balance <xsl:value-of select="/members/member/name[ (string-length(../member_data/title) > 0) and (../member_data/balance > 0) ]"/> Can also do this within the path like so: <xsl:value-of select="/members/member [member_data/title!= '' and member_data/balance > 0]/name"/>

28 6/3/2016 8:44 PM 28 of 35 28) Combine XPaths If you want all nodes that match two different paths, you can combine two paths results with " " Example, all dates of interest, when members joined or left: //join //left returns 4 dates in a copy-of, just the first date in a value-of (try it).

29 6/3/2016 8:44 PM 29 of 35 29) Review: How to build an XPath Identify your starting location ("/" or no value, for the current context node) State your next step with one of these: an element name, matches all element nodes at the current context with that followed by an attribute name, matches all attributes on the current element node with that attribute name (note: you must be on an element, or this matches nothing) invoke an XPath function, for example comment() to identify comment nodes If that step would identify more than one node, you can use a index to denote which one you want, if you only want one; this is done by putting the index number in square brackets. If you don't index, the first one is taken if one must be chosen. If that step would identify more than one node, you can use an XPath predicate to pick from among them; this is done by putting a boolean test in square brackets, like the index. If it's just an XPath, then it's an existence test. If you want to take another step through the tree, add a "/" and return to the previous step (this will limit you to a single node match at the previous item, if there was more than one the first one is taken) At any point, if there is no match found, then your node set is empty/you have no node. You will just keep on

30 6/3/2016 8:44 PM 30 of 35 with an empty set from that point forward.

31 6/3/2016 8:44 PM 31 of 35 30) Troubleshooting If you get errors, check your syntax: matching square braces matching quotes correctly embedded quotes

32 6/3/2016 8:44 PM 32 of 35 31) Troubleshooting If you get no results, check your path: does it identify elements correctly (case matters!) does it mark attributes correctly are attributes on the correct elements is it in the correct context

33 6/3/2016 8:44 PM 33 of 35 32) Troubleshooting, continued Build up your XPath one step at a time, checking results with copy-of to ensure the right parts of the XML input tree are identified Test an XPath used in another XSL element with both value-of and copy-of to see if it is identifying the correct node or nodes.

34 6/3/2016 8:44 PM 34 of 35 33) Resources XPath W3schools XPath 1.0 Zvon.org XPath FreeFormatter.com

35 6/3/2016 8:44 PM 35 of 35 34) Your Turn Using value-of, get the name of the member who is President, using a comparison test to check for President. Using value-of, get the number of calories in the lemon pudding. Using copy-of, get all of the first names' contents. This requires an XPath shortcut and a function. Find all of the contents in pudding.xml that contain the word "or". Did you find just the 3 words, more, or fewer matches? Why?