What's the difference between an element and a node in XML?

Question

I'm working in Java with XML and I'm wondering; what's the difference between an element and a node?

Tarmac

Great comment from forums.asp.net/t/443912.aspx/1#443940: The same as between fruit and apple. Every XmlElement is XmlNode, but not every XmlNode is XmlElement. XmlElement is just one kind of XmlNode. Others are XmlAttribute, XmlText etc. – Gauger

An Element is part of the formal definition of a well-formed XML document, whereas a node is defined as part of the Document Object Model for processing XML documents. – Filariasis

It might be worth pointing out that XML itself does not use the term "node", and it defines an element as something with a start tag and end tag. The question is not about terms defined "in XML" it is about terms defined in a tree model representing parsed XML: probably but not necessarily the DOM model. – Lucilucia

Answer 1

The Node object is the primary data type for the entire DOM.

A node can be an element node, an attribute node, a text node, or any other of the node types explained in the "Node types" chapter.

An XML element is everything from (including) the element's start tag to (including) the element's end tag.

Groundhog

Now that I understand the answer...The convention is stupid. The words should be the other way around. In natural English language an 'element' is something which is the most basic building block, out of which everything else is built. i.e. an element in natural English is more general... – Files

you mean a node is more general? – Nagle

@SamSvenbjorgchristiensensen I always refer to <p>s and <div>s as p elements and the div elements – Ghibelline

@Juan Mendes: That's what they are according to the DOM, but Sam's point is that the DOM considers nodes more basic (primitive) than elements, when "element" actually refers to the most basic building block in English. – Anthea

@SamSvenbjorgchristiensensen that's not quite accurate. Elements can be broken down further into 'constituent parts' like protons, neutrons and electrons, which in turn can be broken into quarks, neutrinos, etc. It's better to understand what a 'node' means in graph theory, and then you'll understand why the XML designers chose that name (the DOM is just a hierarchical graph). – Kempis

@LesHazlewood I was referring to gist of the word 'element' across its various meanings, rather than chemical element in particular (when the term element came into use for chemicals, people did not know that they were further divisible). It's all a bit subjective, so I can't say you're right or wrong. I draw my definitions from en.wiktionary.org/wiki/element#Noun – Files

@SamSvenbjorgchristiensensen I personally trust Merriam-Webster over Wiktionary (who knows the credentials of a wiki-based author!). Their definition favors the 'constituent part' semantics, chemical or not. Cheers! – Kempis

@LesHazlewood Actually, the word "element" was used to describe physical elements (hydrogen, helium, etc) because they did think those things were indivisible. It was only much later they found out they were wrong - far too late to change the name ; ) I agree with Sam, the way they named and differentiated dom elements vs nodes is confusing and poorly thought through (as much of the html spec is). – Flunkey

@BT your argument would hold water if the XML spec committee lived in ancient Greece :) They did not, and as such, the modern (dictionary) definition of element that (clearly) represents constituent parts makes sense. Add that with graph theory knowledge of nodes, and there's really not much room for interpretation. – Kempis

i think there should not be a distinction between a Node and an Element. Some nuances just add unnecessary complexity and this is one of them – Tory

Answer 2

Different W3C specifications define different sets of "Node" types.

Thus, the DOM spec defines the following types of nodes:

• Document -- Element (maximum of one), ProcessingInstruction, Comment, DocumentType
• DocumentFragment -- Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference
• DocumentType -- no children
• EntityReference -- Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference
• Element -- Element, Text, Comment, ProcessingInstruction, CDATASection, EntityReference
• Attr -- Text, EntityReference
• ProcessingInstruction -- no children
• Comment -- no children
• Text -- no children
• CDATASection -- no children
• Entity -- Element, ProcessingInstruction, Comment, Text, CDATASection, EntityReference
• Notation -- no children

The XML Infoset (used by XPath) has a smaller set of nodes:

The Document Information Item

Element Information Items

Attribute Information Items

Processing Instruction Information Items

Unexpanded Entity Reference Information Items

Character Information Items

Comment Information Items

The Document Type Declaration Information Item

Unparsed Entity Information Items

Notation Information Items

Namespace Information Items

XPath has the following Node types:

• root nodes
• element nodes
• text nodes
• attribute nodes
• namespace nodes
• processing instruction nodes
• comment nodes

The answer to your question "What is the difference between an element and a node" is:

An element is a type of node. Many other types of nodes exist and serve different purposes.

Alethaalethea

Answer 3

A Node is a part of the DOM tree, an Element is a particular type of Node

e.g. <foo> This is Text </foo>

You have a foo Element, (which is also a Node, as Element inherits from Node) and a Text Node 'This is Text', that is a child of the foo Element/Node

Bibbye

This short example gives me more understanding then the selected answer. – Considering

Answer 4

A node can be a number of different kinds of things: some text, a comment, an element, an entity, etc. An element is a particular kind of node.

Atmosphere

Answer 5

As described in the various XML specifications, an element is that which consists of a start tag, and end tag, and the content in between, or alternately an empty element tag (which has no content or end tag). In other words, these are all elements:

<foo> stuff </foo>
<foo bar="baz"></foo>
<foo baz="qux" />

Though you hear "node" used with roughly the same meaning, it has no precise definition per XML specs. It's usually used to refer to nodes of things like DOMs, which may be closely related to XML or use XML for their representation.

Distasteful

Answer 6

An xml document is made of nested elements. An element begins at its opening tag and ends at its closing tag. You're probably seen <body> and </body> in html. Everything between the opening and closing tags is the element's content. If an element is defined by a self-closing tag (eg. <br/>) then its content is empty.

Opening tags can also specify attributes, eg. <p class="rant">. In this example the attribute name is 'class' and its value 'rant'.

The XML language has no such thing as a 'node'. Read the spec, the word doesn't occur.

Some people use the word 'node' informally to mean element, which is confusing because some parsers also give the word a technical meaning (identifying 'text nodes' and 'element nodes'). The exact meaning depends on the parser, so the word is ill-defined unless you state what parser you are using. If you mean element, say 'element'.

Hoff

The word does occur: "(i.e., each leaf node in the syntax tree for the regular expression)". It's in a non-normative appendix, but nevertheless it does occur. There the term is used as node in the parse tree. – Avalokitesvara

Even if one considers that the XML definition does not mention nodes, the Document Object Model (DOM) defined for programmatic interpretation and manipulation of XML (by the same standards organization) does indeed define and use the term "node". This answer does not help to differentiate the terms and it does not help to just ignore the various uses by asserting that they mean the same thing. – Simulation

The OP clearly had in mind the terms "element" and "node" as used in tree models such as the DOM, and failed to understand that these are DOM concepts rather than XML concepts. It's misleading to say that the concepts depend on which parser you are using, since they are defined in many standardised data models for XML including the DOM, the Infoset, and the XDM model. – Lucilucia

Answer 7

A node is the base class for both elements and attributes (and basically all other XML representations too).

Moyra

Answer 8

Element is the only kind of node that can have child nodes and attributes.

Document also has child nodes, BUT
no attributes, no text, exactly one child element.

Sibell

Answer 9

A node is defined as:

the smallest unit of a valid, complete structure in a document.

or as:

An object in the tree view that serves as a container to hold related objects.

Now their are many different kinds of nodes as an elements node, an attribute node etc.

(Edited 2024-02-24 to remove a link, which pointed to a completely irrelevant IBM web page)

Settle

Answer 10

Now i know ,the element is one of node

All node types in here"http://www.w3schools.com/dom/dom_nodetype.asp"

Element is between the start tag and end in the end tag

So text node is a node , but not a element.

Sainted

Answer 11

An element is a type of node as are attributes, text etc.

Vermifuge

Answer 12

XML Element is a XML Node but with additional elements like attributes.

<a>Lorem Ipsum</a>  //This is a node

<a id="sample">Lorem Ipsum</a>  //This is an element

Scopoline

I don't assume you have any source for this claim? For example the XML standard defines the term "element" being either an empty element tag or everything from and including the start tag to and including the end tag. A start tag and empty element tag does not need to have any elements. Both your examples are elements. The term "node" is defined elsewhere, in DOM which is about an object model and not in the text itself. – Avalokitesvara

Answer 13

node & element are same. Every element is a node , but it's not that every node must be an element.

Objection

As "it's not that every node must be an element", the claim "node & element are same" is wrong. – Yogi

Besides your description is wrong, it's not very useful either. The only thing you're correct about is that there is some difference between the terms, but the question was what difference there is. – Avalokitesvara