is a set of strict rules that specify well formed xml documents involving tags namespaces and attributes etc these variable parameters give meaning in the context of the target program to data contained within what is actually a text document one that as we shall see below can be visualized with any word processing system an xml document 39 s purpose however is to be parsed and processed by an xml processor that tests the document for validity and sorts out and conditions the data in the xml document and for example feeds it to an associated application in order to interface non sap or u201c foreign u201d components with the above referenced centralized monitoring architecture xml is exploited as an interface or data transport mechanism for the external data supplier particularly those that would otherwise be unable to access the traditional standard interface for fully compliant sap components in order to be a valid xml document according to xml 1 0 the document must contain a document type declaration to define constraints on the logical structure and to support the use of predefined storage units an xml document is valid if it has an associated document type declaration and if the document complies with the constraints expressed in it the xml document type declaration contains or points.