XQuery Terminology

Nodes

There are seven kinds of nodes in XQuery:

Root: it is the topmost element of the document with child elements below it.
Element (<tagname> ... </tagname>): these type follows the root node and can contain attribute in it.
Attribute (<tagname attribute="value">): this can be assigned below the element or root node.
Text: it represents the text written inside an element node.
Namespace: it matches namespace for all the nodes. This is defined at the beginning of the document in which the root element is declared.
Processing-instruction (<? ?>): this specifies the instruction for the application and can be used anywhere in the XML document.
Comment (<comment> </comment>): this node specifies the comment part for the particular code that is not processed by any programming language compiler.

note

XML documents are treated as trees of nodes. The root of the tree is called the document node (or root node).

Consider this example:

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>
<comment>This is a comment</comment>

We have that:

<bookstore> is the root element node.
<author>Tutorial Reference</author> is an element node.
Tutorial Reference is a text node.
lang="en" is an attribute node.
<?xml-stylesheet type="text/css" href="style.css"?> is a processing-instruction node.
<comment>This is a comment</comment> is a comment node.

Atomic values

Atomic values are nodes with no children or parent.

For example:

Tutorial Reference  
  
"en"

Relationship of Nodes

Parent

Each element and attribute has one parent which is a top element of the respective element or attribute.

For example, the <book> element is the parent of <title>, <author> and <year> elements

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>

Children

Element nodes can have zero, one or more children.

For example, <title>, <author> and <year> elements are children of the <book> element

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>

Siblings

Nodes that have the same parent are known as siblings.

For example, <title>, <author> and <year> elements are siblings because they have the same parent element <book>

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>

Ancestors

The parent of a node or the parent of the parent, etc. is specified as the ancestor.

For example, the <book> element is the parent of <title>, <author> and <year> elements

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>

Descendants

The children of a node or the children of children, etc. are specified as the descendants.

For example, <book>, <title>, <author> and <year> elements are descendents of the <bookstore> element

<?xml version="1.0"  encoding="UTF-8"?>  

<bookstore>
    <book>
        <title lang="en">A Great Book</title>
        <author>Tutorial Reference</author>
        <year>2022</year>
    </book>
</bookstore>

XQuery Terminology