Explain xpath and xquery in simple terms

Question

I am new to programming. I know what XML is. Can anyone please explain in simple terms what xpath and xquery do Where are they used?

Answer 1

XPath is a way of locating specific elements in an XML tree.

For instance, given the following structure:

<myfarm>
  <animal type="dog">
    <name>Fido</name>
    <color>Black</color>
  </animal>
  <animal type="cat">
    <name>Mitsy</name>
    <color>Orange</color>
  </animal>
</myfarm>

XPath allows you to traverse the structure, such as:

/myfarm/animal[@type="dog"]/name/text()

which would give you "Fido"

XQuery is an XML query language that makes use of XPath to query XML structures. However it also allows for functions to be defined and called, as well as complex querying of data structures using FLWOR expressions. FLWOR allows for join functionality between data sets defined in XML. FLWOR article from wikipedia

Sample XQuery (using some XPath) is:

declare function local:toggle-boolean($b as xs:string) 
as xs:string 
{
    if ($b = "Yes") then "true"
    else if ($b = "No") then "false"
    else if ($b = "true") then "Yes"
    else if ($b = "false") then "No"
    else "[ERROR] @ local:toggle-boolean"
};

<ResultXML>
    <ChangeTrue>{ local:toggle-boolean(doc("file.xml")/article[@id="1"]/text()) }</ChangeTrue>
    <ChangeNo>{ local:toggle-boolean(doc("file.xml")/article[@id="2"]/text()) }</ChangeNo>
</ResultXML>