Full Form of DTD:
Document Type Definition
DTD Full Form is Document Type Definition. A set consisting of mark-up declarations that are used for defining the type of a document for the mark-up languages of the SGML family is referred to as a DTD or Document Type Definition. The mark-up languages that comprise the SGML family include HTML, XML, and SGML. In an XML document, the legal building blocks are defined with the help of DTD. It also helps by defining the structure of a document through a list of attributes and right elements. There are two ways of declaring a DTD, which is: external reference and inline or inline declaration.
A DOCTYPE or a document type declaration is used for associating a DTD with an SGML or XML documents. The DOCTYPE is mentioned near the XML document’s beginning, in doctypedecl, which is a syntactic fragment. The DTDs can be declared either in an external or internal subset. In the case of the declaration of the DTDs in the internal subset, the declarations themselves form a portion of the document’s DOCTYPE. In the event of the declarations in the external subsets, the declarations are present in an entirely separated text file.
A system identifier or a public identifier is used for calling the external subset. For reading this subset, the programmer may not need the programs that are used for reading documents. A DoS or Denial of Service can be created with the help of an XML DTD. The XML Parser can be sent to a resource located externally for creating DoS. The dot net framework offers a property that allows the skipping of the prohibition of the DTD parsing for the same reason. The XML files consisting of DTD declarations cannot be opened by the latest versions of the applications of the Microsoft Office due to the same reasons.