"ABSTRACT Software is a critical component of the design@ construction@ and operation of HVACR systems and equipment in buildings@ yet seldom does one software application communicate information to another. The lack of compatibility between applications leads to information about the building and its systems being re-interpreted and re-entered for each application causing inefficiency and even information loss. Draft Guideline 20@ titled ""XML Definitions for HVACR"" is attempting to establish a common data exchange format for the description of commodity data and HVACR information using eXtensible Markup Language@ XML. The research project focused on four of the twelve Use Cases described in draft Guideline 20. For each Use Case@ detailed process steps describing the Use Case were elaborated. From the detailed process steps@ transfers of information were extracted showing the groups of data that were needed to communicate between various parties. After analysis@ the 107 Data Groups identified were named and defined. Using these Data Groups@ three selected existing data models were examined in detail and 4350 Data Elements were identified. Only 37 of these Data Elements were found in all three existing data models."