Techniques are described for exchanging data between software applications, such as project-related data between a project management software application (“PMSA”) and an unaffiliated organizational project tracking software application (“OPTSA”). A mapping and other related information may be defined for the data exchange, such as by defining data fields of the OPTSA database and PMSA data file that correspond, and optionally specifying related information such as additional processing to be performed for various data fields during the data exchange, conditions when a mapping is to be used, ordering information for data fields during import and/or export, preferred data formats for stored values, etc. Also, in some situations round-trip data import/export is performed for a single PMSA data file, which may include tracking whether data entity instances previously existed in the destination in order to support changes to stored inter-relationships between data entity instances.