XPath Jan 14 2019 What is XPath XPath is a syntax used for selecting parts of an XML document The way XPath describes paths to elements is similar to the way an operating system describes paths to files XPath is almost a small programming language it has functions tests and expressions XPath is a W3C standard XPath is not itself written as XML but is used heavily in XSLT 2 Terminology library book chapter chapter chapter section paragraph paragraph section chapter book library library is the parent of book book is the parent of the two chapters The two chapters are the children of book and the section is the child of the second chapter The two chapters of the book are siblings they have the same parent library book and the second chapter are the ancestors of the section The two chapters the section and the two paragraphs are the descendents of the book 3 Paths Operating system XPath the root directory library the root element if named library users dave foo the one file named foo in dave in users library book chapter section every section element in a chapter in every book in the library foo the one file named foo in the current directory section every section element that is a child of the current element the current directory the current element the parent directory parent of the current element users dave all the files in users dave library book chapter all the elements in library book chapter 4 Slashes A path that begins with a represents an absolute path starting from the top of the document A path that does not begin with a represents a path starting from the current element Example email message header from Note that even an absolute path can select more than one element A slash by itself means the whole document Example header from A path that begins with can start from anywhere in the document Example header from selects every element from that is a child of an element header This can be expensive since it involves searching the entire document 5 Brackets and last A number in brackets selects a particular matching child counting starts from 1 except in Internet Explorer The function last in brackets selects the last matching child Example library book 1 selects the first book of the library Example chapter section 2 selects the second section of every chapter in the XML document Example book chapter 1 section 2 Only matching elements are counted for example if a book has both sections and exercises the latter are ignored when counting sections Example library book chapter last You can even do simple arithmetic Example library book chapter last 1 6 Stars A star or asterisk is a wild card it means all the elements at this level Example library book chapter selects every child of every chapter of every book in the library Example book selects every child of every book chapters tableOfContents index etc Example paragraph selects every paragraph that has exactly three ancestors Example selects every element in the entire document 7 Attributes I You can select attributes by themselves or elements that have certain attributes Remember an attribute consists of a name value pair for example in chapter num 5 the attribute is named num To choose the attribute itself prefix the name with Example num will choose every attribute named num Example will choose every attribute everywhere in the document To choose elements that have a given attribute put the attribute name in square brackets Example chapter num will select every chapter element anywhere in the document that has an attribute named num 8 Attributes II chapter num selects every chapter element with an attribute num chapter not num selects every chapter element that does not have a num attribute chapter selects every chapter element that has any attribute chapter not selects every chapter element with no attributes 9 Values of attributes chapter num 3 selects every chapter element with an attribute num with value 3 The normalize space function can be used to remove leading and trailing spaces from a value before comparison Example chapter normalize space num 3 10 Axes An axis plural axes is a set of nodes relative to a given node X Y means choose Y from the X axis self is the set of current nodes not too useful self node is the current node child is the default so child X is the same as X parent is the parent of the current node ancestor is all ancestors of the current node up to and including the root descendant is all descendants of the current node Note never contains attribute or namespace nodes preceding is everything before the current node in the entire XML document following is everything after the current node in the entire XML document 11 Axes outline view Starting from a given node the self preceding following ancestor and descendant axes form a partition of all the nodes if we ignore attribute and namespace nodes library book chapter chapter section paragraph paragraph section chapter chapter book book library chapter 2 self chapter 2 preceding chapter 2 following chapter 2 ancestor chapter 2 descendant 12 Axes tree view Starting from a given node the self ancestor descendant preceding and following axes form a partition of all the nodes if we ignore attribute and namespace nodes library ancestor book 1 preceding chapter 1 self chapter 2 following book 2 chapter 3 section 1 descendant paragraph 1 paragraph 2 13 Axis examples book descendant is all descendants of every book book descendant section is all section descendants of every book parent is every element that is a parent i e is not a leaf section parent is every parent of a section element parent chapter is every chapter that is a parent i e has children library book 3 following is everything after the third book in the library 14 More axes ancestor or self ancestors plus the current node descendant or self descendants plus the current node attribute is all attributes of the current node namespace is all namespace nodes of the current node preceding is everything before the current node in the entire XML document following sibling is all siblings after the current node Note preceding sibling and following sibling do not apply to attribute nodes or namespace nodes 15 Abbreviations for axes none is the same as child is the same as attribute is the same as self node X is the same as self node descendant or self node child X is the same as parent node X is the same as parent node child X is the same as descendant or self node X is the same as descendant or
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