The document object model (DOM) is a programming API for HTML and XML documents. With its help, you can assess the logical structure of a document and how it is manipulated. The term document in the document object model is used in a broad sense. XML is used to represent different information stored in diverse systems and most of it will be seen as data instead of a document. However, XML presents this data as a document, and DOM is used to manage the data. 

With the help of DOM, programmers can create documents, navigate the structure, and add, modify, or delete content. The document object model is a way of representing the webpage in a structured hierarchical manner so that it will be easy for the programmers and users to slide through the document. With DOM, you can easily access and manipulate tags, IDs, classes, attributes, and elements of HTML using commands or methods provided by the document object. DOM provides a standard programming interface that can be used for different applications. The document object model can be used with any programming language. 

By using the DOM Javascript can manipulate the HTML and CSS on the web page and also add certain behaviors to the HTML elements. A document object model is an API that interacts with HTML or XML data. 

Why is DOM required?

HTML is a programming language that is used to provide structure to most web pages and Javascript is used to add behavioral elements to web pages. When a web page is opened, an HTML file is loaded on the browser but the javascript is unable to understand the document directly. That’s why a document is created so that javascript can understand HTML files. DOM represents the HTML document but now it uses objects which makes it easier for javascript to understand the HTML document. While the document object model in javascript is unavailable now javascript can understand HTML or XML documents. 

Javascript can now understand DOM easily. Earlier it couldn’t understand HTML tags like <h1>H</h1> but now it understands them as objects like h1 in DOM. Javascript can access each object with the help of different functions. 

Structure of DOM

DOM is like a structural forest of a website. People use the term structured model to describe the tree-like representation of a document. Each branch of a tree has multiple nodes and each node is connected to different objects. A node can have event listeners, they are triggered once an event takes place. If any two DOM implementations are used to create a representation of the same document, the structure model will be identical. All the relationships between different objects will remain the same. This property of DOM is called a structural isomorphism. 

Documents are only able to be modeled because of objects. The model includes the structure of the document, the behavior of the document, and the objects of which it is composed like tag elements with HTML attributes. 

Properties of DOM

A document object model has multiple properties which help users assess the logical structure of data. In the document object model, there are many objects which make DOM resourceful. Some of them are: 

Window object:

A window object is an object of the browser which is why it is always at the top of the hierarchy. With this object, the type of browser used by the user will be clear. It is like an API that is automatically manufactured by the browser and is used to set or access the properties of a browser. 

Document Object:

When an HTML document is loaded into a window it is transformed into a document object. The document object possesses various unique features that refer to other objects. By using the document object, you can modify the content of a web page. If you need to access a particular HTML element, you have to start by getting access to the document object. Document object is the property of window object. 

A document object has many different properties: 

  • Form object: Form objects are represented by the form tags. 
  • Link object: A link object is represented by link tags. 
  • Anchor object: The anchor object is represented by the href tags. 
  • Form control elements: A form has many control elements which helps user make choices on a web page. Some examples will be text areas, checkboxes, radio buttons, buttons, select buttons, etc. 

In an abstract data model, the model is centered around crucial data. However, in object-oriented programming languages, the data is contained in objects to hide it. 

This protects your data from external manipulation which is why object-oriented programming languages are generally better when it comes to security. A web design company is more likely to use an object-oriented programming language if security is an important factor. The functions that are connected with the objects determine how the objects can be manipulated or used. 

The document object model has two parts, DOM Core and DOM HTML. The DOM Core is used to represent the functionality used for XML documents, and it serves as a foundation for DOM HTML. 

Origins of the Document Object Model (DOM)

The document object model started as a specification to allow javascript to understand a web page. Dynamic HTML existed before the document object model and can be considered as an ancestor which served the same function. However, when the document object model working group was created, it was joined by vendors of other domains like HTML and XML editors and document repositories. Most of these vendors had collaborated with Standard Generalized Markup Language (SGML) before the development of XML. This means that the document object model has been highly influenced by SGML Groves and the HyTime standard. 

Some of these vendors have now developed their own object models for documents. This made it easy to provide APIs for SGML/XML editors or document repositories. These new object models have also influenced the current document object model. 

Things for DOM will keep on changing as technology is upgraded. If you have a web design company it is best to stick with options that are the most popular and user-friendly. 

Interfaces and implementations of DOM

The DOM contains information on interfaces that are used to manage XML or HTML documents. The important thing to realize is that the interfaces are just abstractions. They are the means of specifying a way to access and manipulate an application’s internal representation in a document. 

Having an interface does not mean that the implementation will be concrete. Each DOM application can maintain documents in any way they prefer as long as the interfaces shown in this specification are supported by it. 

Some of the implementations will need to be on existing programs that were created long before DOM existed. The design of DOM avoids any implementation dependencies. 

What DOM is not?

There are many systems that seem like DOM but are actually not related to it. If you want to run a successful web design company, you need to know these differences. 

Do not confuse the following systems or features with Document Object Model (DOM). 

  1. There is no denying that dynamic HTML has strongly influenced the document object model. However, in level 1 it doesn’t implement all of the dynamic HTML. Level 1 is designed to create a solid foundation for this functionality by providing an insightful model of the document itself. 
  2. The document object model is not a binary specification. Document object model programs can be written in the same language as the source code of the application. This ensures compatibility across all different platforms but it does not define any binary form of interoperability. 
  1. The document object model is not a method by which you can preserve objects in XML or HTML. Instead of describing how objects will be represented in XML, the document object model specifies how XML and HTML documents are represented as objects. When these documents are accurately represented as objects, they can be used in an object-oriented programming (OOP) language. 
  2. The document object model is not a model with different data structures. It is an object model which specifies different interfaces. The programming interfaces are able to define logical relationships between different objects. These relationships can be like parent/child relationships. It is extremely important to understand the relationship between different objects if you run a web design company. 
  3. The document object model is not used to define the inner semantics of programming languages like XML or HTML. The semantics of such languages cannot be defined by any document but by those languages themselves. The document object model is just a model which operates with respect to those semantics. If you think you can gain an understanding of the semantics of a programming language by gaining access to DOM, then you are wrong. DOM is not affected by the way you write XML and HTML documents. Any document which is written in these languages can be represented using the document object model. 
  1. There is a misconception among beginners that the document object model (DOM) is a competitor to the Component Object Model (COM). The component object model like COBRA is a way to describe the interfaces and objects. COM is independent of any programming language. The document object model is a set of interfaces and objects designed to work with HTML and XML documents. The DOM has to be implemented using language-independent systems like COM or COBRA. This way of implementation ensures success and efficiency. The document object model can also be implemented by using language-specific bindings like Java or ECMAScript bindings. 
  1. The document object model does not have information about the importance of objects found in the document. It doesn’t know which objects in the document are appropriate and which are not. There is also no knowledge about the context of the objects. 

Levels of Document Object Model

A document object model has many sets of levels. A web design company can only be successful if the employees have intensive knowledge of these different levels. 

  • Level 0: This level provides a different set of interfaces. 
  • Level 1: Level 1 of DOM can be described in two parts CORE and HTML. 

CORE provides low-level interfaces which can be used to represent any document with a legit structure. HTML is useful in providing high-level interfaces that can help in representing HTML documents. 

  • Level 2:

Level 2 has around six specifications such as CORE2, VIEWS, EVENTS, STYLE, TRAVERSAL, and RANGE. CORE 2 is used to extend the functionalities provided by CORE in level 1. VIEWS allow programs to dynamically access and manipulate the content of the document. EVENTS are specific scripts that are activated once the user completes a specific action. 

This event can be the user making a purchase or going to another page. All these events have to be defined before by the programmers so that the users can act. STYLE allows programs to dynamically access and manipulate the content of style sheets. TRAVERSAL allows the programs to dynamically cross the entire content. RANGE allows the program to identify a specific range of content in the document. 

  • Level 3: This level includes five specifications such as CORE3, LOAD and SAVE, VALIDATION, EVENTS, and XPATH. CORE3 is used to extend the functionality of CORE in DOM level 2. 

The LOAD and SAVE specification is used to load the content of the XML document into the DOM document and save the DOM document as an XML document. VALIDATION allows the program to dynamically update the content and structure of the document while ensuring that the document stays valid. EVENTS is used to extend the functionality of the Events specified by DOM in level 2. XPATH is a special path language that can provide you with the access to DOM tree. 


Not everyone knows what the document object model is but developers who focus on developing websites with easier user interfaces have the knowledge. Not only do they know what DOM is but they also use it to analyze the logical structure of data on a web page. This helps them in retrieving crucial information about their website.