Difference between Document Type Definition (DTD) and XML Schema Definition (XSD)

Document Type Definition and XML Schema Definition both contain a set of rules that control the structure and elements of XML files, but they are different in syntax and usage. They check whether an XML document has a valid structure or not. This article will discuss the difference between DTD and XSD.

What is Document Type Definition (DTD)?

DTD stands for Document Type Definition and DTD contains a set of rules that control the structure and elements of XML files. It is used to describe the attributes of XML language precisely. It can be classified into two types namely internal DTD and external DTD. It can be specified inside a document or outside a document. DTD mainly checks the grammar and validity of an XML document.

Features of DTD

It defines the compulsory and optional elements in the XML document.
It validates the structure of the XML document.
It checks for the grammar of the XML document.
It describes the order in which the element occurs.

Advantages of DTD

We can define our own format for the XML files by DTD.
It helps in validation of XML file.
It provides us with a proper documentation.
It enables us to describe a XML document efficiently.

Disadvantages of DTD

DTDs are hard to read and maintain if they are large in size.
It is not object oriented.
The documentation support is limited.
DTD doesn’t support namespaces.

What is XML Schema Definition (XSD)?

XSD stands for XML Schema Definition and it is a way to describe the structure of a XML document. It defines the rules for all the attributes and elements in an XML document. It can also be used to generate XML documents. It also checks the vocabulary of the document. It doesn’t require processing by a parser.

Features of XSD

XSD allows you to create detailed data arrangements with things like nested elements, attributes, and different data types.
Helps you define different kinds of data, like words, numbers, and dates, in XML documents. It allows you to decide how this data should be structured.
You can also decide on default values and rules for elements and attributes in your XML documents.
XSD is good for working with various names in XML, which is useful when you’re creating rules for complex XML files with lots of different names.

Advantages of XSD

XSD schemas are like user-friendly guides for XML data. They tell developers how the data should be structured and the rules it must follow, all without needing extra explanations.
Helps different systems and apps work together smoothly by creating a common language for organizing and checking data.
Lets you set automatic values for missing parts in your data. It’s like having placeholders ready, so if some information is missing, it gets filled in with the default values. This keeps your data consistent.
XSD checks data to make sure it’s correct, stopping any mistakes from getting into XML documents.
Provides different data types, like primitive data types, derived data types, and user-defined data types. This variety helps keep data organized and dependable.

Disadvantages of XSD

Creating and maintaining XSD schemas can be complex, especially for intricate XML structures.
Understanding and working with XSD can be challenging for those new to XML and related technologies.
Data validation using XSD can introduce a performance overhead, especially for large XML documents.

Difference Between DTD and XSD

DTD	XSD
DTD are the declarations that define a document type for SGML.	XSD describes the elements in a XML document.
It doesn’t support namespace.	It supports namespace.
It is comparatively harder than XSD.	It is relatively more simpler than DTD.
It doesn’t support datatypes.	It supports datatypes.
SGML syntax is used for DTD.	XML is used for writing XSD.
It is not extensible in nature.	It is extensible in nature.
It doesn’t give us much control on structure of XML document.	It gives us more control on structure of XML document.
It specifies only the root element.	Any element which is made global can be done as root as markup validation.
It doesn’t have any restrictions on data used.	It specifies certain data restrictions.
It is not much easy to learn .	It is simple in learning.
File here is saved as .dtd	File in XSD is saved as .xsd file.
It is not a strongly typed mechanism.	It is a strongly typed mechanism.
It uses #PCDATA which is a string data type.	It uses fundamental and primitive data types.

Conclusion

Document Type Definition (DTD) and XML Schema Definition (XSD) both specify and validate the structure of XML documents, but they differ significantly. DTD utilises its own syntax, and is simpler but less powerful, with no support for namespaces or data types. On the other hand, XSD, which is based on XML, provides comprehensive data type support, full namespace handling, increased flexibility, and extensibility, making it the ideal choice for complex XML applications.

Frequently Asked Questions on DTD and XSD – FAQs

Why XML schema is powerful than DTD?

The XML Schema gives a more detailed definition of the data structure than the DTD, mandating that is a string and is an integer.

Is mandatory to have a DTD or XSD for an XML file?

Why is DTD prohibited in this XML document?

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