Document Type Definition (DTD)

• is an XML-based Schema Definition Language (SDL)
• defines the structure and the legal elements and attributes of an XML document

• superseded by XSD

XML Schema Definition (XSD)

• a more powerful alternative to DTD

Web Service Definition Language (WSDL)

• is an XML-based Interface Description Language (IDL)
• that is used for describing the functionality offered by a web service

XML Path Language (XPath)

• is an XML-based language for finding any element on the web page using XML path expression