What is a Document Type Definition (DTD)?
A DTD defines what elements and attributes are legal inside an XML document. The strength of a DTD is that it describes a standard for XML documents and what elements should be inside them. Different organizations can share the same DTD so that the XML will work for each side. When XML is transferred from one system to another, elements must match the ones on the new system or software applications won’t work. This differs from html; browsers can display files containing multiple errors, but that is not the case with XML. Choosing a DTD allows an XML file to be validated and ensured that it is operational. DTDs can distinguish which data will be parsed for tags inside the elements, but ensuring that elements contain particular data types means a more advanced approach is necessary. The alternative to DTDs are schemas, which let elements be bound to certain data types. More information on schemas is found below. DTDs are less complicated than schemas, which makes them a good option if d
