(1) (EXternal Data Representation) A data format developed by Sun that is part of its networking standards. It deals with integer size, byte ordering, data representation, etc. and is used as an interchange format. Different systems convert data to XDR for sending and from XDR upon receipt.

(2) (XML-Data Reduced) An XML schema language from Microsoft prior to the W3C XML schema. XDR was released in 1999 as a working schema as part of Microsoft's BizTalk initiative. XDR supports data typing and XML namespaces. See XML schema and XML.