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CG0119 Web Database Systems Using XPath to Navigate & Filter XML (via SimpleXML) . XPath. What is it? w3c standard for… Navigating through an XML document Filtering & finding information Includes… Expressions for navigating to parts of an XML document
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CG0119 Web Database SystemsUsing XPath to Navigate & Filter XML (via SimpleXML)
XPath • What is it? • w3c standard for… • Navigating through an XML document • Filtering & finding information • Includes… • Expressions for navigating to parts of an XML document • The standard includes functions (e.g. for string & date manipulation) • Used in XSLT – we used some XPath path expressions last week…!!!
XPath Expressions • What are they? • Path expressions are a means of selecting nodes (or sets of nodes) from an XML document • They consist of… • A path to the nodes/node sets • A predicate (optional) • Syntax • Without a predicate: • Nodenames, separated by a forward slash (/) • Predicates: • Predicates are placed inside [ ]
Root node Child of root node Example xml document student.xml <?xml version="1.0"?> <students> <student> <studentCode>P283746</studentCode> <forename>Anabela</forename> <surname>Domingues</surname> <studyTypeID>P</studyTypeID> <startYear>2004</startYear> </student> <student> <studentCode>M928493</studentCode> <forename>Ann</forename> <surname>Devon</surname> <studyTypeID>U</studyTypeID> <startYear>2002</startYear> </student> ... </students> Children of student
Examples: XPath Expressions • What would be the path expression to navigate to the startYear node? ‘/students/student/startYear’ • What would be the path expression to select the startYear node where the startYear = 2002? ‘/students/student/startYear[. = “2002”]’ --- OR --- ‘/students/student[startYear = “2002”]/startYear’ www.w3schools.com/xpath/xpath_intro.asp has more details on & examples of path expressions
Example: Multiple Predicates • What would be the path expression to select student nodes where the startYear = 2002 and the studyTypeIdD= U? '/students/student[startYear=2003][studyTypeID = "U"]' www.w3schools.com/xpath/xpath_intro.asp has more details on & examples of path expressions
Name Student Code Ann Devon M928493 … … Fiona Murray M828827 XPath & simpleXML Example The aim of the example used in the following slides is to list data in a XHTML table for all students who started at University in 2002 e.g.
XPath & simpleXML – PHP Code Steps involved in this example: • Create an instance of a simpleXML class by loading the XML file • Construct the query expression • Call the XPath method to execute the query • Loop through the result set
Steps 1 to 3: simpleXML & XPath Objects // Create a new simplexml instance loading xml file $studentsXML = simplexml_load_file('student.xml'); // Construct an XPath expression, // including a predicate in this instance. $qry = '/students/student[startYear = "2002"] '; // call the simplexml xpath method $students = $studentsXML->xpath($qry);
echo "<table border=\"1\">\n"; echo "<tr><td>Student Code</td><td>Name</td></tr>\n"; echo "<tr>\n"; echo "<td>{$student->studentCode}</td>\n"; echo "<td>{$student->forename} "; echo "{$student->surname}</td>\n"; echo "</tr>\n"; echo "</table>\n"; Step 4: Loop Through Query Result Set // iterate through the students returned by the xpath query foreach ($students as $student) { } echo " {$student->studentCode} \n"; echo " {$student->forename} "; echo "{$student->surname} \n";
Summary • XPath is a w3c standard for • Navigating through an XML document • Filtering & finding information • Path expressions navigate to a particular node or node-set and they may include predicates
Recommended Reading http://www.zvon.org/xxl/XPathTutorial/General/examples.html - Xpath tutorial http://www.rpbourret.com/xml/XPathIn5.htm - XPath in 5 paragraphs! http://www.w3schools.com/xpath/ - w3schools XPath tutorial & reference *
