Overview of DTD

Document Type Definition(DTD) includes the formal specification that describes the structure, legal elements, and attributes of an XML Document. We can say that it acts like a rulebook that specifies the structure and relationship between the elements of an XML Document. It also checks the validity and vocabulary against the grammatical rules of XML language.

Moreover, it defines the elements, their syntax, and rules to use them in an XML document. Hence, a valid and well-formed XML document must conform to the DTD specifications. Below is the syntax of DTD in a ‘sample.dtd’ file:

<!DOCTYPE rootElement [
    <!-- DTD rules are defined here →
    Declaration 1…
    Declaration 2…
]> 

Where the DOCTYPE is a delimiter, rootElement is the starting element parsed by the parser, and the square brackets define the list of declarations.

DTD Components

Markup Languages play a very important role in encoding and standardizing information that is shared over the web. XML (Extensible Markup Language), being one of those languages, provides a set of rules to encode data in the document which is both human as well as machine-readable.

For this, XML uses a unique specification norm to define the structure of a document which is called a Document Type Definition (DTD). In this article, we have covered every minute detail about DTD and its components. So, without any delay, let us delve deep into the DTD Components.

Table of Content

  • Overview of DTD
  • What are DTD Components?
  • Examples of DTD Components
  • Features of DTD Components
  • Advantages of DTD Components
  • Disadvantages of DTD Components
  • Conclusion

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Overview of DTD

Document Type Definition(DTD) includes the formal specification that describes the structure, legal elements, and attributes of an XML Document. We can say that it acts like a rulebook that specifies the structure and relationship between the elements of an XML Document. It also checks the validity and vocabulary against the grammatical rules of XML language....

What are DTD Components?

DTD components are the building blocks of the XML Document which are described by the DTD. These are nothing but the XML Components that are described in DTD in terms of syntax, validation, and their order in XML files. The various DTD Components are described below:...

Examples of DTD Components

Example of DTD Element:...

Features of DTD Components

Define the structure of the document: Each DTD component contributes to the structuring of the XM document which helps to properly define the structure of the XML file. Define the data type: They allow us to properly define the data type of each element in the document so that components can be used appropriately. Provide complete information on the document: They clearly state the optional as well as compulsory attributes and elements in the document so that we can maintain the information easily. Define the order of the Elements: DTD component specifies the order in which the elements occur within a document along with their frequency. It also specifies whether they can be reused or not....

Advantages of DTD Components

Provide a structured approach: DTD specification helps us to follow a step-by-step process to define and validate the XML document. Promote reusability: With Entity elements, they make the elements reusable which allows us to use a modular approach. Thus, the components can be used again without redefining them. Define our document format: It allows us to define our own XML format so that the developer or users can easily understand the information in the XML document. XML document is validated properly: It avoids all the flaws in the document by checking it against the grammatical rules so that the information can be parsed properly....

Disadvantages of DTD Components

DTD components are not Object-Oriented: DTD follows a procedural approach to define the structure and relationship between the elements in a document. Thus, it is not possible to define the elements as Objects for complex document Support text string data type: In DTD, we can store and validate the text-string data type due to which diverse data types cannot be supported in the document Don’t support namespaces: Namespaces are present in DTD due to which we can encounter naming conflicts or naming collisions in the larger documents. Provide limited cardinality options: You can use only zero or more occurrences (*), one or more occurrences (+), and optional occurrences (?) in DTD which makes it less flexible....

Conclusion

DTD Components describes the building blocks of the XML document and the rules to validate them as per the standards. Each component in DTD has some utility in the XML documentation, to describe the attributes and entities, whether they are mandatory or optional, their order, and their occurrences in the document....