Week 10: XML

(1) Extensible Markup Language, or XML, is allows a set of rules for encoding documents to be read by both humans and machines.  (2) XML has a series of entities that contain one or more logical elements, which are what mark the start and end of each of the parts of an interchanged document. (3) Document Type Definitions, or DTDs, allow users of XML to check that the document occurs in a valid place within the interchanged data stream, but are not required for XML. (4) XML was not designed to be a standardized coding system, such as HTML is.  (5) XML is a formal language that can be used to pass information about the component parts of a document onto another computer system.  (6) XML is different from other markup languages in the fact that it clearly identifies the boundaries of every part of a document. (7) An XML file typically consists of three different types of markup; an XML processing instruction, a document type declaration, and a fully-tagged document instance.  (8) The processing instruction identifies the version of XML being used, how it is coded, and whether there are external files.  (9) The document type declarations can either contain a markup declaration in an internal subset [between square brackets] or an external subset [referencing a file containing markup declarations].  (10) Finally, a document instance consists of a root element that matches the assigned document type in the document type declaration.  (11) If all three components are present, and the document instance conforms to the rules defined in the document type definition, the document is said to be valid.