A data set is one complete data record, which is none other than a table row (which can be viewed on the IBExpert Table Editor / Data page). It encompasses a single set of information, such as, for example, one customer address or one employee record.
In a relational database the physical sequence of data sets is irrelevant.
Duplicate data sets or records (i.e. double rows) are not allowed in a relational database, as this is, in effect, storage of redundant information (see Database Normalization).