XML Magic Structures of XML Data elements in XML are delineated by discrete tags, but these tags are not always simply a random structure. There are files and structures used to determine and indicate the way a given message is put together and how various applications will handle it. Tags allow discrete bits of data to be marked for processing. Tags can also carry additional information for processing and formatting data, and we shall discuss some of that as we proceed here.
Tags can be unique to the implementation, or in a data dictionary for many implementations.
Qualifiers may be embedded in tags as a value to enhance uniqueness or carry further information for identification or processing. It should, however, be noted the fact Tags must be interpretable by humans for debugging, their content does NOT need to be readable by humans in lieu of system processing. Tags are therefore used to allow a computer system to parse an XML file for processing, and NOT as an aid to use of the data without a system. The DTD The DTD, or Document Type Definition, defines the structure of the document to be interchanged between trading partners It needs to be common to the interchange, but does not necessarily need to be a standard. It can reside anywhere on the Internet accessible to all parties to the transaction.