A Document Type Definition (DTD) is a structured description of the structure and content of an XML document. It is used to define the rules according to which an XML document must be created in order to be accepted as a valid document in a specific XML-based system.
The main features of a DTD are
Elements and attributes: A DTD defines the acceptable elements and attributes in an XML document, as well as their hierarchy and relationships to each other.
Data types: It specifies the data types that may be used for elements and attributes, including text, number, date, etc.
Rules and constraints: DTDs can contain rules and constraints that define how elements and attributes may be used and what values they can take.
DTDs are often used to ensure interoperability between different XML-based systems, as they clearly define the structure and semantics of XML documents. They are used, for example, in web development for the validation of XHTML documents, in data transfer between different systems and in the documentation of XML schemas.
