A Document Type Definition (DTD) is a set of rules that defines the structure and legal elements of an XML document, ensuring validity against its structure. There are two types of DTDs: internal and external, each serving to validate XML documents and define element relationships. While DTDs are simple and widely supported, they have limitations such as restricted data types, lack of namespace support, and lower extensibility compared to XML Schema.

1. DOCUMENT TYPES DEFINITION
.
DTD (Document Type Definition) is a set of rules or a blueprint
that defines the structure and the legal elements and attributes
of an XML document. It ensures that the XML file conforms to a
specific structure.
There are two types of DTDs:
1. Internal DTD: The rules are declared within the XML file itself.
2. 2. External DTD: The rules are declared in a separate file and
referenced within the XML file.

2. .
Purpose of DTD:
1.To define the allowed elements, attributes,
and their relationships.
2.To ensure that XML documents are valid by
comparing them against the DTD.
3.To provide a way to define default values
for attributes.

3. Advantages of DTD:
• 1. Simple and easy to understand: DTDs use a straightforward syntax,
making them easier for beginners to grasp compared to XML Schema
(XSD).
• 2. Well-supported: DTDs are widely supported across many XML
parsers and editors, ensuring compatibility.
• 3. Compact: DTD files are generally concise, requiring fewer lines of
code compared to XML Schema, especially for small documents.
• 4. Embedded or external: DTD can be embedded directly within the
XML file or referenced externally, providing flexibility for document
validation.

4. Disadvantages of DTD
• 1. Limited data types: DTD only supports basic data types such as strings
(PCDATA), which limits its ability to enforce more complex data validation like
numbers, dates, or patterns. XML Schema (XSD) offers richer type support.
• 2. No namespace support: DTD does not have native support for XML
namespaces, making it difficult to manage complex documents that require
multiple vocabularies.
• 3. Limited extensibility: DTD lacks many features found in more modern
alternatives like XML Schema, such as the ability to define complex structures,
inheritance, or more granular control over validation rules.
• 4. Non-XML syntax: Unlike XML Schema, which uses XML syntax itself, DTD uses a
separate non-XML syntax, making it inconsistent with XML’s overall structure.

5. Enriiii Media/Thank u