Abstract: The present invention provides copybook flat data conversion with inline transformation. Specifically, a streaming intermediary formatted data message is generated as a result of converting/transforming a flat file format (non-XML (Extensible Markup Language) format), such as raw fixed-length field COBOL (Common Business-Oriented Language) copybook format or the like. The streaming intermediary format is not fully held in memory, but rather is directly transformed/converted, using XSLT (Extensible Stylesheet Language Transformations) processing, into a target format, such as structured XML or the like. By directly streaming the intermediary format to the XSLT process without holding the entire data message in memory, the present invention utilizes less memory and, as such, less memory is needed to be reclaimed.