Not all fields of a given Luminate Online constituent record will correspond to fields in the external system database, and vice versa. The first step in defining any data synchronization is identifying the fields in each database which should be synchronized, and creating a formal mapping between them. You can do this in a spreadsheet, mapping each field of Luminate Online data to its corresponding field in the external database and specifying whether the field is to be downloaded, uploaded, or both. This map is a key project artifact that should be kept current throughout the development and test process.
If you are using a middleware framework to develop the synchronization process, the framework will specify the map file format, likely in an XML schema.