Harvesting the data refers to the process of extracting the data from the external system and copying it into the data set tables in the InterAction database. The data set tables act as a staging area. They hold the data until you start the transformation process.
After successfully transforming the data, Application Collaboration purges the data from the data set tables. Your harvesting routine should refill these tables each time it is run.
Normally, your harvesting routine collects all the data the first time. Once the initial data has been successfully transformed into InterAction, the harvesting routine should only gather the changes. In some cases this is not possible, such as when you are using the Replace Data option for additional fields. For more details, see Data Harvesting Recommendations.