XML and data tranfer

XML ~ eXtensible markup language ~ an open standard for defining data and its elements, making it readable in a variety of platforms, by a variety of applications. XML facilitates data definition thru its use of tags, similarly to HTML. however, XML defines the structure of the data, whereas HTML defines the appearance of the data. a complete set of XML elements make up an XML document.

two levels of ‘correctness’ of XML exist: 1. well formed ~document obeys the rules required by the XML standard, and, 2. valid ~ document conforms to specific rules of the specific XML application.

DTDs and schemas provide ways of validating XML documents. DTDs ~ document type definitions ~ inflexible; do not allow for specification of attributes and element types. Schemas ~ more flexible; more complex; XSD and XDR. 1. XSD ~ XML Schema Definition language ~ defines a type of XML document in terms of constraints upon what elements and attributes may appear, their relationship to each other, what types of data may be in them, and other things. It can be used with validation software in order to ascertain whether a particular XML document is of that type; more powerful, more complex. 2. XML-Data Reduced schemas ~ similar to XSD, but its element defined within the top-level element of the schema; no premable for declarations, instead using namespace declarations.