The metalanguage is not encoded in binary, but consists of plain text characters. This is often ASCII encoding and is therefore readable by both humans and machines. The property of extensibility represents one of the major differences from HTML. The latter metalanguage is only suitable for documents on the Internet and is strongly oriented towards written elements. XML, on the other hand, is extensible and has no definitive vocabulary. Temporal information, security elements and even graphical components, amongst others, can be captured in XML.
What is the advantage of XML files? In addition to the extensibility already mentioned, these text files offer indispensable independence. On the one hand, data exchange can take place across platforms and is not tied to any specific implementation. Specific sublanguages can be developed on the basis of XML, depending on the application. In order to maintain a certain degree of consistency in data exchange, it is recommended to define the sentence structure and semantics via a document type definition (DTD for short) or another schema language. These rules ensure a consistent structure across a wide variety of files.
XML is the base language for numerous other W3C standards. For example, there are query languages such as XPath and XQuery, and a transformation language (XSLT). The important further development of HTML is also based on XML (XHTML). The language also forms the basis for the most important web services standards (such as SOAP, WSDL and BPEL4WS) and the languages of the Semantic Web (such as RDF and OWL).
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